Two goals from Clayton Donaldson, a player Paul Dickov tried to sign before he joined Brentford, inflicted a painful defeat which leaves Latics in the lower reaches of npower League One.
The clinical finishing from Donaldson, one of the division’s leading marksmen, was effectively the difference between two evenly-contested teams as he scored his 16th and 17th goals of the campaign.
It was a disappointing afternoon for Latics who suffered an eighth home league loss as the cheer provided by Jose Baxter signing a new two-and-a-half-year contract pre-match quickly disappeared.
Latics’ manager described it as a "nearly day" believing that if his side had played with the same intensity they displayed at Nottingham Forest they could have upset the promotion-chasing Bees.
Dickov said: "It was really disappointing after last week. We were lack lustre and we didn’t show the same effort and desire as they did to come back against Scunthorpe and against Nottingham Forest.
"We weren’t quite at it. I don’t know whether it was the euphoria of last week or Jose signing just before kick-off, but we were flat. There was a lack of tempo with our passing and a lack of tempo when we were closing down players.
"In saying that, we had more possession and more shots than Brentford, but I could not see us winning the game today.
"Brentford had two shots on goal from Donaldson who is a quality striker, Dean Bouzanis has not have a save to make and we have ended up losing 2-0.
"It was a nearly game – we nearly won the ball back, nearly got crosses in the box and nearly got shot.
"Brentford are a good team with lot of good, powerful players and you have to give them credit.
"I still felt it was a game we could have won. There wasn’t much in the game and if we had stepped up an extra 10-per-cent we could have got something out of it."
Latics made one change from the team which kicked off in the FA Cup with Budweiser tie at Nottingham Forest as Carl Winchester was selected to replace captain Dean Furman who is away at the African Cup of Nations.
Reece Wabara retained his right-back spot after extending his loan hours before the game.
There was a huge cheer just before the start when it was announced Baxter had signed a new long-term deal.
The now-familiar chant 'Jose Baxter Baby' reverberated around the ground and that was followed by a bright start as Matt Smith had an early chance, but could only direct his header straight at keeper Simon Moore.
They were then dealt a blow when Donaldson put Latics ahead in the fifth minute with a terrific header from Harry Forrester’s left-wing cross.
Latics came back strongly as Smith, Baxter and Cliff Byrne all had chances to equalise, but none was able to hit the target.
That flurry of activity came in an electrifying opening 11 minutes which was followed a lull in the action.
Latics finished the opening half brightly as Winchester fired disappointingly wide after featuring in a super passing build up while Baxter chipped wide.
Baxter kept foraging just behind lone front man Smith and early in the second period curled a shot which forced a diving save from Moore.
Brentford then had a spell when Adam Forshaw had three chances in as many minutes, but fired either wide or over.
Latics brought on Daniel Taylor and Kirk Millar for Robbie Simpson and Cliff Byrne respectively as they went three at the back in pursuit of an equaliser.
Baxter had another creditable effort which forced a stretching catch from Moore while Millar made a forward raid before firing narrowly wide.
Latics were caught taking risks as they went for a leveller as Donaldson struck again in the 82nd minute to seal victory.
Substitute Sam Saunders square the ball from the right to Donaldson who was completely free in front of goal as he slotted home a low shot from 12 yards.
Connor Hughes replaced Winchester late on as Latics finished the game strongly.
Taylor was released by Smith in stoppage time and his fierce shot was beaten to safety by Moore.
Baxter also had a shot deflected for a corner in the five minutes of added time, but Latics were unable to find a route to goal.
Latics (4-4-1-1): Bouzanis; Wabara, Byrne (Millar 77), M’voto, Grounds; Croft, Winchester (Hughes 84), M’Changama, Simpson (Taylor 71); Baxter; Smith. Subs (not used): Cisak, Brown, Tarkowski, Mellor.
Brentford (4-1-4-1): Moore; Logan, Craig, Dean, Bidwell; Kiernan (Diagouraga 59); Donaldson, Forshaw, Douglas, Forrester (Barron 75); Trotta (Saunders 79). Subs (not used): Gounet, Hodson, Reeves, Hayes.
The goals: Donaldson (5,82) for Brentford.
Bookings: Baxter (57) for Latics. Donaldson (66), Diagouraga (68) for Brentford.
Referee: Mr A Haines.
Attendance: 4,615 (208 visitors).