Bringing in the veteran goalkeeper has proved to be a crucial move for the Portuguese coach after the Australian excelled against Liverpool and Atletico Madrid
Chelsea have spent a combined 69 million pounds on Andre Schurrle, Willian and Nemanja Matic since Jose Mourinho rejoined the club, as well as bringing in Samuel Eto'o and Mohamed Salah on what are sure to be handsome wages.
But the signing that has kept the Blues in the hunt for the Premier League title and UEFA Champions League glory was the unheralded free transfer of veteran goalkeeper Mark Schwarzer.
Having left Fulham at the end of last season, Australian supporters were keen to see the then-active Socceroo, with the 2014 World Cup on the horizon, secure another spot as a first-choice number one.
Premier League and championship clubs were mentioned, and a move to the A-League was even mooted in some quarters.
When the former Middlesbrough stalwart surprisingly popped up at Stamford Bridge, the move was greeted with a mixture of delight and apprehension. Fans were pleased to see a great of modern Australian football join a genuine powerhouse club, particularly after being denied the chance to sign for Arsenal in 2010.
But there were also significant doubts about how much playing time he would receive. They were valid concerns indeed with Schwarzer, until last weekend, having made just a handful of appearances in all competitions. Such was the impact of his new watching brief that he called time on his international career in November, pre-empting a possible exclusion from Ange Postecoglou's World Cup squad.
Schwarzer finally made his Premier League debut for Chelsea in the surprise loss at home to Sunderland last Saturday. The result aside, it was a good job the 41-year-old was afforded an opportunity to become reacquainted with the demands of top-flight football.
Three days later he was called on to replace an injured Petr Cech in the cauldron of a Champions League semi-final away to Atletico Madrid, acquitting himself well as the west London side escaped from Estadio Vicente Calderon with a 0-0 draw.
On Sunday he underlined the enormous value of having a trustworthy back-up goalkeeper, producing an assured display - and a number of top-draw saves - to deny Liverpool in a 2-0 win at Anfield which has thrown open the title race.
Matic, Schurrle, Willian and Salah all played a part in the smash-and-grab raid, but they couldn't have done it without Schwarzer between the sticks. Would the questionable Hilario, a peculiar relic of Mourinho's first spell in charge, have performed so effectively with equally little match-practice? Doubtful.
Long-suffering Liverpool supporters have more reason than ever to curse Mourinho after the Portuguese orchestrated a defensive, counterattacking master-class to potentially wreck their cherished title dream.
But they shouldn't only blame his time-wasting tactics and uncanny ability to shutdown even the most free-flowing of opponents. The roots of the Reds' downfall on Sunday can be traced all the way back to the shrewdest decision of all - handing a one-year deal to one of the Premier League's oldest and safest pair of hands.