The Robins had played second fiddle for the majority but raised their game in the last half-hour to arrest a run of five defeats in their last six matches.
Looking to build on their win at Birmingham in their last league outing on New Year's Day, Wigan were quickly into the ascendancy with the visitors on the back foot.
Despite dominating the ball for the opening quarter, the home side failed to work much in the way of goalmouth action.
Fortunately for Bentley, the ball flew back past him but just past the post.
Diedhiou then netted the best goal he will ever score in his life, a top corner volley from 30 yards which David Marshall couldn't get anywhere near.
Sadly for the big striker, the flag had been up for a while and the 'goal' was disallowed.
Wigan started the second period the way they had begun the first, on top but failing to ask probing enough questions.
A swift counter-attack from Wigan then saw Dowell find Nathan Byrne, whose header at the far post flew wide.
Bristol City had offered little up to this point, but almost took the lead just after the hour mark when Diedhiou again sent a brilliant strike goalwards.
Somehow, Marshall got a fingertip on to the ball, diverting it on to the crossbar and over for a corner.
Garner immediately tested Bentley with a good header, while Gelhardt sent a 20-yard strike inches over.
But it was the visitors who took control of the game with two goals inside the space of three minutes to shock the DW Stadium.
With 13 minutes to go, Paterson went through one-on-one before sliding the ball underneath the advancing Marshall.
Then, two minutes later, Paterson played in Diedhiou, who lashed home into the far corner with the goalkeeper helpless.