Aston Villa ended a run of 11 league games without a win by beating Watford.
Agbonlahor has been a reliable source of goals for Villa
Both sides had lacked a cutting edge in front of goal with Milan Baros the main culprit for the Villa as he failed to convert two one-on-one chances.
But the deadlock was broken when an angled Gavin McCann shot struck Gavin Mahon on the six-yard line and went in.
The goal deflated a valiant Watford and they conceded a second in injury-time when Gabriel Agbonlahor shrugged off Danny Shittu and slotted home.
The defeat was harsh on Watford against a Villa side who had started with the lack of belief, confidence and authority that saw them go into the game bottom of the Premiership form table.
606 DEBATE: Give your thoughts on the match
There was plenty of effort from the home side but attacks regularly broke down because of stray passes and Watford tried to capitalise.
The visitors mounted some early pressure only to miss the creativity and quality in the final third of the pitch to take advantage of a fragile Villa.
But the Midlanders gradually realised that they could end their recent poor run against the Premiership's basement club and had the chances to take the lead without showing the conviction to do so.
Mackay (l) battle with Villa striker Angel
Gareth Barry cut inside a defender and looked set to score with a left-foot strike only for Foster to stick out an arm and divert the strike against the post.
At the other end, Hameur Bouazza sent a rasping volley just high before keeper Thomas Sorensen tipped a Will Hoskins strike over his crossbar as the Hornets finished the first half on the front foot.
Villa's fortunes and play did not improve after the break and the frustration of the home fans grew as the game wore on.
Hoskins again went close for the visitors when he flicked a shot just wide as Villa struggled amid the obvious frustration being vented by their supporters.
Baros could have lifted the Villa gloom when he was played through on goal by Agbonlahor but was denied when the on-rushing Foster came out of his goal to save.
Another chance for Baros saw him send an angled shot wide with keeper Foster to beat as Watford were almost caught out by Agbonlahor as they waited for an offside flag which failed to arrive.
Foster was an irritating barrier who continually thwarted Villa but he could do nothing when McCann's shot went in off Mackay and then Mahon before Agbonlahor sidefooted in during injury time.
Aston Villa boss Martin O'Neill:
"I'm not so sure what I feel," he said. "Obviously, I'm relieved and delighted we won.
"I think we deserved to win had a no of clear cut chances in the game.
"I thought under pressure we did very well. I thought our approach play was very good we just could not finish anything off."
Watford manager Aidy Boothroyd:
"I won't pretend it's not hard. I want to win every match and we go into each game aiming for exactly that.
"Not winning is difficult to take, particularly this season. I'm not a big believer in luck - at least I wasn't before this season.
"What we have to do now is get on with it."
Aston Villa: Sorensen, Bardsley, Mellberg, Cahill, Bouma, Davis, McCann, Barry, Agbonlahor, Angel (Berger 72), Baros (Samuel 79).
Subs Not Used: Taylor, Hughes, Ridgewell.
Booked: Davis, Mellberg.
Goals: Mahon 86 og, Agbonlahor 90.
Watford: Foster, Mariappa, Mackay, Shittu, Stewart, Smith, Mahon, Francis, Bouazza (Powell 70), Priskin (Henderson 54), Hoskins (Ashikodi 80).
Subs Not Used: Lee, DeMerit.
Ref: P Walton (Northamptonshire).