The striker came off the bench midway through the second and netted the winner with 14 minutes remaining to keep Atletico on track for a third-placed finish in La Liga
Fernando Torres came off the bench to seal a 1-0 win for Atletico Madrid against shot-shy Villarreal on Wednesday.
It was Torres' fifth goal since rejoining Atletico in January and came with a sizeable slice of help from the unfortunate Eric Bailly.
The Ivory Coast defender stumbled under pressure in the 74th minute, allowing Torres to bear down on goal, round Sergio Asenjo in the Villarreal goal and calmly slot past scrambling defenders on the line.
Atletico's triumph strengthens their grip on third place in La Liga as they move to 75 points - six above Sevilla with four games remaining.
By contrast, Villarreal's promising campaign is grinding to a halt in dire fashion, with a winless run that stands at 10 games in all competitions. Marcelino's team have failed to find the net in six of their past seven outings.
Gerard slid a pass to Joel Campbell inside the penalty area after two minutes but the on-loan Arsenal forward was unable to open his account for Villarreal, firing straight at Atletico goalkeeper Jan Oblak.
In-form forward Antoine Griezmann looked sharp from the outset and, shortly after he had penalty claims rejected under a challenge from Bojan Jokic, Asenjo saved well to deny the France international from an acute angle in the 15th minute.
Villarreal keeper Asenjo was scrambling when Arda Turan's looping header dropped narrowly wide and Atleti midfielder Koke thudded a strike into the advertising hoardings following excellent hold-up play from Mario Mandzukic.
But Villarreal were not allowing their visitors to dominate and they were unlucky not to be ahead in the 34th minute.
Victor Ruiz's close-range header from Antonio Rukavina's free-kick was brilliantly kept out by Oblak before Diego Godin cleared Gerard's follow-up off the line.
Both sides continued to probe with intent after the interval but clear chances dried up, although Griezmann might have done better when he headed Jesus Gamez's perfectly flighted left-wing cross off target.
Diego Simeone sent on Torres and Saul for Mandzukic and Turan in an attempted to freshen up Atletico's attacking options but initially to no avail.
Gerard timed his run well to break into the Atleti box on the end of Jaume Costa's pass but lost his footing at the crucial moment, and Godin was on hand once more to block the follow-up strike from Moi Gomez.
Villarreal would live to rue that miss as Torres showed a merciless, clinical instinct to exploit Bailly's moment to forget.
Griezmann could have doubled the margin of victory before Asenjo suffered a leg injury when catching a cross to leave the field early in clear discomfort.
Marcelino's men could have salvaged a point in stoppage time but Mario and then Costa fired off target as their barren run in front of goal rumbled on.