Ivory Coast striker Didier Drogba pounced in the 67th minute to put Chelsea in front and late goals from Florent Malouda and Frank Lampard ensured they remain in the hunt to become only the seventh English team to win both competitions in the same season.
It was Drogba's 32nd goal of the season but until he struck with typically clinical efficiency, the FA Cup holders had laboured against a side they hammered 7-1 in the league at Stamford Bridge a fortnight ago.
Carlo Ancelotti's side looked lethargic and out of sorts in a largely forgettable opening half.
The state of the Wembley pitch was the biggest factor as the semi-final got underway, with players from both sides failing to keep their feet.
Villa, still smarting from that heavy drubbing, settled much quicker than Chelsea.
But Chelsea had their isolated moments. Joe Cole, attempting to persuade watching England boss Fabio Capello that he is worth a place in his squad for the World Cup finals, sent an angled drive just wide from 20 yards in the 11th minute.
But Villa had more intensity about their game and, although the players continued to be hampered by the greasy surface, they possessed more menace.
James Milner almost put them in front in the 14th minute when his 25-yard drive flashed inches wide of Petr Cech's right-hand post.
But the biggest talking point of the opening half, even eclipsing the state of the pitch, was a Villa penalty appeal that was firmly rejected by Howard Webb.
Gabriel Agbonlahor looked to have pulled the shirt of John Obi Mikel before the Villa striker went down under his challenge.
Referee Webb dismissed their appeals, much to the chagrin of coach Martin O'Neill in the Villa technical area.
Villa's high-tempo game was causing Chelsea all kinds of problems and the league leaders needed a last-gasp header from captain John Terry to prevent John Carew from finishing off a fine cross by Stewart Downing.
But in the 34th minute, Villa were thankful for a superb block by Stephen Warnock as Florent Malouda's cross provided Drogba with an opening.
Chelsea countered through the lively Cole who forced Villa goalkeeper Brad Friedel into a fine save at his near post when Warnock's poor header fell to the Chelsea winger.
Villa striker John Carew, who had been marshalled superbly by Terry for much of the game, was just wide from a corner by Downing in the 46th minute.
But Villa's game fell away, just as it had done in the league game a fortnight ago, and Chelsea, buoyed by a half-time pep-talk from Ancelotti, set about their opponents for the first time in the game.
Deco sent a half-volley wide of the target in the 50th minute and moments later Cole just failed to get on the end of a Drogba cross at the near post.
Cole made way for Salomon Kalou in the 64th minute and two minutes later the substitute played a part in Chelsea's opener.
Kalou found the rampaging Drogba with a clever through-ball but he was foiled by a challenge from Richard Dunne.
But Chelsea made Villa pay from Malouda's corner. Dunne could only head the ball straight to Terry and his mis-hit shot fell to the unmarked Drogba, who steered it home from six yards.
It was his fifth goal in competitive matches at Wembley and broke Villa's resistance completely.
O'Neill's side, faced with lifting themselves in the final 20 minutes, huffed and puffed without troubling Cech in the Chelsea goal.
It was Chelsea who finished the stronger and they booked a place in their third FA Cup final in four years through Malouda in the 89th minute.
Frank Lampard fed substitute Michael Ballack on the right wing and the German crossed superbly for Malouda to sweep the ball home at the far post.
Lampard scored a third from close range in added time but by then it was all academic, with Chelsea's double dream still very much alive.