After almost incessant second-half pressure from Chelsea, during which they hit the woodwork twice and saw the defensive linchpins of Gareth Southgate and Ugo Ehiogu repel numerous other assaults on the Villa goal, Roberto Di Matteo swung over a corner from the Chelsea right, Gianluca Vialli flicked the ball on and Flo met it firmly with his forehead to condemn Villa to only their second League defeat of the season.
The win takes Chelsea up to third place but, while Villa missed the opportunity to stretch the Premiership lead they have held for three months, they will rarely encounter a side as good as Chelsea, playing as well as they did last night.
After picking up only two points from the last four matches the jury might still be out on the championship credentials of John Gregory's Villa team, but it would be wrong for anyone to read too much into last night's result.
"There's nothing to be ashamed of in that performance," Steve Harrison, Gregory's assistant, rightly pointed out. "It was a hard game played at a very high tempo."
Vialli, Chelsea's player-manager who scored a hat-trick when the sides met in the Worthington Cup six weeks ago and who chose to start a League game for only the second time this season, said: "To score in the last minute you have to be a bit lucky, but if you keep working hard at least you can say you tried, and I think we deserved to win."
Chelsea were simply inspired. With Villa relying on the pace of Julian Joachim, for once preferred to Stan Collymore, the onus was on Chelsea to take the initiative. This they did despite the first clear chance falling to Joachim, who steered his shot wide after outsprinting Michael Duberry.
For Chelsea there were half chances aplenty but it was 29 minutes before Villa's defence was breached for the first time, Southgate bringing Di Matteo down on the edge of the area and Gianfranco Zola curling the free- kick beyond Villa's six-man wall and past a helpless Michael Oakes.
Only a minute later, though, Villa were level after a move of bewildering speed and first-time passing involving Dion Dublin, Ian Taylor and Joachim, who fed Lee Hendrie as he burst into the six-yard box and produced a cool, side-footed finish.
The first 45 minutes were hectic but the next 20 were unrelenting and it was all Chelsea. A more compassionate referee than Alan Wilkie might have been tempted to stop the contest with Villa taking so much punishment, but once again good chances were at a premium for Chelsea.
The best of them fell to Franck Leboeuf when Ehiogu was beaten in the air at Di Matteo's corner, but the Frenchman's glancing header hit the underside of the Villa bar and bounced away to safety.
Shortly after that Flo came on to replace Zola as Chelsea went in search of a second wind. Again Villa held them at bay, but in the final minute of normal time, Graeme Le Saux's cross-shot evaded everyone and rebounded off the inside of the post. After that Villa must have thought they had survived - but Flo had the final word.
Chelsea (4-4-2): De Goey, Ferrer, Leboeuf, Duberry, Le Saux; Petrescu, Babayaro (Poyet, 80), Desailly, Di Matteo; Vialli, Zola (Flo, 65). Substitutes not used: Wise, Lambourde, Hitchcock (gk).
Aston Villa (5-3-2): Oakes; Watson, Ehiogu, Southgate, Barry, Wright; Hendrie, Taylor, Thompson; Joachim (Collymore, 82), Dublin. Substitutes not used: Grayson, Charles, Lescott, Ghent (gk).
Referee: A Wilkie (Chester-le-Street).Reuse content