Roman Abramovich brought the Blues back to the top of English football with their first title in 50 years, after a spell of lavish spending helped end Manchester United's dominance in the Premier League.
There were plenty of mistakes made before Abramovich took over but after he acquired the club in 2003, the errors became more costly.
Below, Goal investigates Chelsea's 15 worst signings of all time.
BOGARDE | From Barcelona | Free | 2000
Winston Bogarde could top any list in world football for bad signings. The Dutchman arrived on a free transfer after spells as a bit-part player at AC Milan and Barcelona but he was a colossal financial burden because of his wages.
Bogarde joined Chelsea at 29 and earned £40,000-a-week, which amounted to a huge £2m a season, and this was before Chelsea became super rich under the ownership of Abramovich.
The defender managed only four starts during his four-year stay in which 11 of his 12 appearances came in his first season at Stamford Bridge.
How could any professional footballer justify making so much money for doing nothing? Allow Bogarde to explain...
"I used to be poor as a kid, did not have anything to spend or anything to play with," the former Ajax starlet stated. "This world is about money, so when you are offered those millions, you take them.
"Few people will ever earn so much. I am one of the few fortunate people who do. I may be one of the worst buys in the history of the Premiership, but I don't care."
Bogarde was forced to quit the game after leaving Chelsea, as he unsurprisingly failed to find another club.
TORRES | From Liverpool | £50m | 2011
Fernando Torres became the most expensive player to move between two British clubs when Chelsea paid Liverpool £50m for their star striker on a dramatic deadline day in January 2011 to Chelsea.
The Spain international was a shadow of his former self at Stamford Bridge, clearly burdened by the great weight of responsibility that his vast price tag brought. He was the target of ridicule for opposition fans and the media as he suffered a dramatic decline.
It took him 903 minutes to score for the Blues and he eventually left the club, for nothing, when AC Milan made his loan move permanent in 2015 only to then be immediately allowed to join Atletico again.
SHEVCHENKO | From AC Milan | £30m | 2006
Chelsea announced themselves as a new footballing superpower with the signing of Andriy Shevchenko from Milan for £30m.
The move was masterminded by Abramovich and Chelsea's then chief executive Peter Kenyon, whom the club had poached from Manchester United.
Shevchenko struggled to adapt to a physical style of play in English football, though, and it quickly became clear that the 29-year-old was past his best. His £121,000-a-week wages made him the highest earner in the squad but he couldn't even manage to get into double figures in his two years at the club.
Nine goals in 48 Premier League games saw him released 11 months early from his contract when he rejoined Dynamo Kiev for free.
KEZMAN | From PSV | £5.3m | 2004
After Manchester United secured Ruud Van Nistelrooy from PSV in a £19m move in 2001, a new prolific poacher emerged in Eindhoven, Mataja Kezman.
His 105 goals in 122 games alerted Jose Mourinho and Roman Abramovich to another goal-machine but Kezman couldn't replicate Van Nistelrooy's success in England.
Dressed in Chelsea's No.9 shirt, he played 24 league games and scored only four goals in his only season at the club. He did score in the League Cup final against Liverpool in a 3-2 win, so it wasn't all bad, but his career went into free-fall after his spell at Stamford Bridge.
Still, Chelsea somehow managed to recoup the £5.3m that they invested in Kezman when they sold him to Atletico Madrid. Unsurprisingly, the Rojiblancos regretted that decision, as Kezman struggled in Spain too.
BOULAHROUZ | From Hamburg | £8.5m | 2006
Khalid Boulahrouz will go down as one of Chelsea's toughest ever players but he proved that aggression isn't the only attribute needed at the top of the game. The Dutchman was part of the Hamburg defence that conceded only 30 goals in 34 games in 2005-06 before moving to the Blues but he failed to continue his great record.
Boulahrouz was bought for £8.5m by Mourinho's Chelsea and he was brought in to be a utility man in an already strong defence. He strangely wore the No.9 shirt that was vacated by Hernan Crespo but then only made 13 appearances for the club.
He still managed to rack up 5 yellow cards and one red card as he failed to compete with John Terry and Ricardo Carvalho for a starting spot. Even when Carvalho was injured, he failed to get in, with Michael Essien used as a make-shift centre back ahead of him.
MUTU | From Parma | £15.8m | 2003
Adrian Mutu was an exciting signing as he arrived from a great Parma team to become the main man in a Blue shirt. He was one of Abramovich's first signings but he will go down as one of the club's most controversial players.
Gianfranco Zola left Chelsea to be replaced by Mutu but he couldn't replicate the genius shown by his predecessor due to a breakdown in relationship with Jose Mourinho.
It got worse, much worse, and in September 2004 he failed a drugs test for cocaine and was subsequently released on 29 October 2004. The FA gave him a seven-month ban and a £20,000 fine.
Ten years of legal proceedings as Chelsea sued their former player for a breach of contract. Mutu got back to his best after departing Chelsea and it was ultimately sad that off-field distractions ended his hopes of showing his quality in the Premier League.
WRIGHT-PHILLIPS | From Man City | £21m | 2005
Shaun Wright-Phillips, arguably England's most promising player at the time, joined Chelsea in 2005 for £21m. His move from Manchester City to London proved to be a risk and he was inconsistent in his first season, earning only 15 starts in an already strong Chelsea side.
He ended up missing out on the 2006 World Cup in Germany and he ultimately rejoined Manchester City for a fee thought to be around £8.5m. He made 125 appearances for Chelsea but almost half of them were from the bench in what ended as an expensive mistake.
VERON | From Man United | £15m | 2003
Juan Sebastian Veron was a truly great player before his arrival in England. However, the £28.1m signing from Lazio flopped at Manchester United before Claudio Ranieri offered the Argentine the opportunity to kick-start his career at Stamford Bridge.
The fee was only £15m this time around but Veron struggled even more in London and only made five league appearances over the duration of his four-year contract.
He had loan spells at Internazionale and Estudiantes but England, sadly, never got to see his true greatness.
AMBROSETTI | From Vicenza | £6.2m | 1999
Gabriele Ambrosetti was dubbed "the Italian Ryan Giggs" by Gianluca Vialli upon signing for Chelsea in 1999.
He only spent one year at Stamford Bridge, though, making just 23 appearances for the Blues before spending the next three seasons out on loan..
Chelsea ultimately let him go for free to Piacenza, in 2003. He never regained the form that convinced Chelsea to sign him.
SUTTON | From Blackburn | £10m | 1999
Chelsea beat Tottenham, Arsenal and Aston Villa to the £10m signing of Chris Sutton from relegated Blackburn Rovers in 1999. Sutton was a Premier League champion and an England international but he struggled throughout his time in west London.
The fee was the third highest paid between English clubs, falling just below Alan Shearer's transfer from Blackburn to Newcastle United and Dwight Yorke's move from Aston Villa to Manchester United.
Sutton scored only three goals for Chelsea, with one coming against Skonto Riga, and another against third division Hull City.
He was sold within the year and Chelsea brought in Jimmy Floyd Hasselbaink and Eidur Gudjohnsen to replace him. Sutton revitalised his career at Celtic, while Chelsea also went on to bigger and better things.
STANIC | From Parma | £5.6m | 2000
Mario Stanic was unveiled alongside both Hasselbaink and Gudjohnsen but he didn't go on to secure the same legendary status as the other two.
The Croat started his Chelsea with a wonder-goal, scoring with a stunning 35-yard volley against West Ham United on the opening day of the 2000-01 Premier League season.
However, he subsequently suffered an injury against Aston Villa that would keep him out for five months and he ended up being plagued by fitness problems before eventually being forced to retire at the age of 32.
FLECK | From Norwich | £2.1m | 1992
Robert Fleck was a Norwich City hero but his exit from the club was controversial as the Canaries were outraged after he missed a photoshoot to talk to Chelsea in London.
Chelsea blew their budget of £2.1m on a man that they believe that could fire them to league success for the first time in decades. Upon bringing in Fleck, Ian Porterfield, the then Chelsea manager said: "It's a great deal for us." It wasn't.
He still gained cult status from the Chelsea support who were chanting for him 10 years after he departed!
MITCHELL | From Feyenoord | £200k | 1988
Dave Mitchell was a hero in a pioneering era for Australian soccer, primarily due to the fact that he got the better of Diego Maradona in a World Cup play-off in 1993.
However, his playing days petered out after his distinctly underwhelming stint at Stamford Bridge, during which he made only eight appearances before moving to NEC Breda.
It must be said, though, that Mitchell's cause wasn't helped by the fact the manager who signed him, the legendary John Hollins, left soon after the Aussie's arrival.
DE LUCAS | From Espanyol | FREE | 2002
Chelsea signed Enrique De Lucas from Espanyol on a free transfer in 2002, only a year before Roman Abramovich took ownership of the club. It was a strange move from the club who quickly realised that he was nowhere near good enough to wear the club's badge.
After just 21 starts, his Chelsea career was over and he was hastily moved on to Alaves after only a year at the club. De Lucas sued Chelsea two years after leaving the club and the case was settled out of court just a few months later.
DEL HORNO | From Athletic Club | £8m | 2005
Asier del Horno is famous for being the guy who produced a knee-high tackle on a 19-year-old Lionel Messi. He was sent off but the Champions League flashpoint was perhaps proof that his £8m move to England was never going to work out for him.
The Spain international won the Premier League in his only season at the club but Chelsea made a loss on him as they sold him to Valencia for £4.8m just 12 months after his arrival.