Liverpool captain Gerrard, who turns 35 on the day of the final, had hoped to bring down the curtain on his Anfield career with a third FA Cup winner’s medal, but instead it is Tim Sherwood’s Villa who will tackle holders Arsenal on May 30.
Philippe Coutinho gave Liverpool the lead at Wembley with a deflected finish in the 30th minute, but in-form Villa striker Christian Benteke equalised six minutes later before Delph snaffled a 54th-minute winner.
It is 15 years since Villa last reached an FA Cup final and 58 years since they achieved the last of their seven successes in the tournament, but victory was just reward for a side who have been transformed since Sherwood succeeded Paul Lambert as manager on Valentine’s Day.
Liverpool, without a trophy since Brendan Rodgers became manager in 2012, could have few complaints about the outcome.
And with seven points now separating them from the Champions League places in the Premier League, Gerrard’s farewell before he joins the Los Angeles Galaxy would appear to be the last significant occasion on their calendar this season.
Villa’s tactic of looking to hit Benteke at the earliest opportunity quickly forced Liverpool back and Simon Mignolet was forced to tip over a shot from Charles N’Zogbia, who was deputising for the injured Gabriel Agbonlahor.
Mid-way through the first half, both sides made changes that were to lead to the opening goal, with Jores Okore replacing the injured Nathan Baker at the back for Villa and Liverpool reverting to a 4-2-3-1 formation.
Minutes later, Okore’s failure to deal with Jordan Henderson’s tame square pass enabled Raheem Sterling to roll the ball into the path of the onrushing Coutinho, who stole into the box and scored via a deflection off Okore’s knee.
– Nerveless Grealish –
Rodgers’s tactical switch had brought immediate dividends, but his side’s lead would not last long.
With Liverpool still readjusting to the new system, Delph raided into space down Villa’s left and cut the ball back for Benteke to steer home his ninth goal in seven games.
Liverpool’s play was crying out for an attacking focal point and at half-time Rodgers sent on Mario Balotelli for Lazar Markovic, which saw Gerrard repositioned in front of the back four in another re-shuffle.
But it was Villa’s football that bristled with attacking intent and nine minutes into the second half they went in front with a neatly worked goal.
Benteke cantered down the left flank and back-heeled the ball to Jack Grealish, Villa’s apparently nerveless 19-year-old playmaker, who rolled a pass into the box for Delph, and the England man stepped inside Dejan Lovren before scoring with his right foot.
It should have been 3-1 just after the hour, but when the ball rolled into Kieran Richardson’s path after Lovren had slid in to thwart Grealish, the former Manchester United man miscued his shot.
Gerrard has made a habit of producing Hollywood endings, but this time the occasion proved beyond him.
He could only steer a free-kick straight at Shay Given and when he headed Coutinho’s corner towards goal with four minutes remaining, Richardson was on hand to head it away.