Riccardo Scimeca gave them a lifeline with 15 minutes left but although Julian Joachim almost squeezed a last-gasp equaliser Villa were unable to recover from the shock of conceding two goals in the opening 31 minutes, both put away in superb style by Leeds' leading scorer, Jimmy Hasselbaink.
Gregory had identified this as a must-win match - indeed, he was looking for nine points from three games to kick-start Villa's season - but after going ahead in only eight minutes, Leeds were able to dictate the play, absorbing Villa's pressure while exploiting the pace and power of Hasselbaink on the counter-attack.
The opening goal stemmed from Ian Harte's throw-in, launching Hasselbaink on a charge through the inside-left channel. Showing considerable strength and balance, the Dutch striker forced his way past teenage defender Gareth Barry before tucking the ball inside Michael Oakes at the near post.
Villa, who had Paul Merson and Gareth Southgate fit to face a Leeds side from which Lee Bowyer and Jonathan Woodgate were the latest absentees, had sprung a major surprise by naming Collymore among the substitutes.
Collymore had been missing for three and a half weeks following his walk- out after refusing to sit on the bench against Fulham in the FA Cup.
"We had a chat at about half past five and agreed to put all the crap to one side," Gregory said. "He has kept himself in good physical shape and with Dion Dublin struggling with his groin injury I needed him as back-up."
But Leeds had bigger surprises for Villa as a makeshift side drawn from an injury- depleted squad went two ahead after 31 minutes, the splendid Hasselbaink again providing the goal.
The Dutchman's first successful effort had been the first by Leeds in a Premiership match for 251 minutes. His second, curled in from a 25-yard free-kick following Gareth Southgate's foul on Willem Korsten, promised more.
Villa had gone close when Joachim, released by Steve Watson's fine pass, delivered a low cross that just eluded Lee Hendrie but later Hasselbaink almost claimed a first-half hat-trick when he shrugged off Alan Wright's challenge only for his shot to come back off the foot of a post.
Leeds found themselves subjected to sustained Villa pressure in the second half and the arrival of Collymore, in place of Dion Dublin with 19 minutes left, proved the catalyst for a fightback by the home side. Villa pulled one back, Scimeca rising at the near post to head home substitute Alan Thompson's corner, but Leeds held firm, Nigel Martyn's alertness denying Joachim an equaliser in the closing moments.
Aston Villa (5-2-1-2): Oakes; Watson, Scimeca, Southgate, Barry (Thompson, 63), Wright; Taylor, Hendrie; Merson; Dublin (Collymore, 71), Joachim. Substitutes not used: Grayson, Samuel, Enckelman (gk).
Leeds United (4-4-2): Martyn; Halle, Wetherall, Radebe, Halle; Haaland, Jones (Granville, 81), Hopkin, Korsten; Hasselbaink, Kewell. Substitutes not used: Wijnhard, Knarvik, Robinson (gk), Smith.
Referee: D Gallagher (Banbury).Reuse content