An out-of-sorts Watford lost ground on the automatic promotion spots after they were beaten 2-0 at Huddersfield.
The Hornets have now dropped down to fifth after an error-strewn display in West Yorkshire.
Town have now won four consecutive home games and are just five points shy of the play-offs.
Huddersfield started the brighter but would not have expected Watford to gift them the opener after just nine minutes.
The veteran's attempted clearance only ricocheted off the shins of Mbenza and into the path of Campbell who gleefully tapped into the empty net.
The Manchester United loanee looked destined to score when the ball fortuitously fell his way just a few yards out, but Schofield was alert enough to keep him at bay.
That miss made it all the more perplexing as to why Troy Deeney was named among the substitutes for Watford, especially after a purple patch that had seen him score in each of his last three outings.
Watford were indebted to Christian Kabasele just after the half-hour mark when the centre-half got back just in time to get a block in on Mbenza.
But from the resulting corner the hosts doubled their advantage – and in comical circumstances, as Mbenza's inswinger was sliced into his own net by Capoue.
It could have got worse just before the interval when Juninho Bacuna's goal-bound effort was well-blocked by the back-tracking Garner.
Carel Eiting tested Foster's concentration just after the restart with a side-footed shot from outside the box.
Watford had plenty of the ball after the break but were finding Town's defence hard to get past. Gray worked his way through just before the hour but was denied by a sprawling save from Schofield.
Capoue blazed over shortly after for the below-par Hornets, who were bossing possession but struggling to make many inroads.
Sub Alex Pritchard blazed over for Town in the final quarter of the game but the two-goal buffer proved more than enough as the hosts ran out worthy winners.