Three of the four play-off places had been decided heading into Sunday's final round of fixtures in the English second tier, with three teams in contention for the final place.
Derby occupied sixth place ahead of the gameweek 46 and were guaranteed the coveted spot if they managed a win over fourth-placed West Brom. However, Middlesbrough lingered just a point behind them before meeting already relegated Rotherham United, while Bristol City sat two points behind Derby heading into their visit to Hull.
Derby and Middlesbrough stayed in the fight for the post-season competition for the entirety of the campaign, while Bristol clawed their way back into the picture following a big improvement in results since the turn of the year.
Although Middlesbrough quickly took a two-goal lead at Rotherham to give themselves a chance of going up, Derby eventually got off the mark against West Brom through Martyn Waghorn and, while the Baggies equalised through Stefan Johansen, goals from Mason Bennett and Harry Wilson secured a 3-1 victory.
Bennett entered the fray in the 65th minute and it proved an inspired substitution as he made a decisive impact with a goal after just five minutes on the pitch. The forward's strike sent the Rams back into sixth place ahead of Boro and, three minutes later, Wilson put the result beyond doubt with a goal from the penalty spot.
Frank Lampard's men will now join Leeds United, West Brom and Aston Villa in the battle for promotion to the top-flight, with Norwich City and Sheffield United already sure of going up by finishing in the top two.
Our Manager. 😍 pic.twitter.com/7D5wTuRUyD— Derby County (@dcfcofficial) May 5, 2019
"It's been a transitional year, which has brought inconsistency, but the run-in has been good for us," Lampard told reporters after his side's crucial win.
"Let's go into the play-offs with no fear and try to upset a few people."
The Championship play-off tournament will begin with West Brom taking on Aston Villa, while third-placed Leeds face Derby - renewing the infamous 'Spygate' rivalry between Lampard and Marcelo Bielsa - before the winner of each tie meets at Wembley to contest the final.
The semi-final first legs will be played next Saturday, with the second legs played the following Tuesday and Wednesday. Then, the final will be played on Monday, May 27.