While the majority of their first-team colleagues concluded a tour of the Far East on Monday, England trio Joe Hart, Joleon Lescott and James Milner enjoyed their first close-season outings alongside France pair Gael Clichy and Samir Nasri.
Holland's Nigel de Jong took the armband and made his second appearance in four days having started Saturday's 2-1 reserve win at Stockport, while the rest of City's line-up was comprised of academy products and Etihad Stadium outcast Roque Santa Cruz.
Having spent the majority of the contest firmly on the back foot, Paul Dickov's League One outfit snatched victory in stoppage time as summer recruit Jonathan Grounds rifled home from Connor Hughes' left-wing corner.
City fell behind in the fourth minute when Clichy passed loosely for Oldham to break and Robbie Simpson clinically slotted his fourth goal of pre-season with a shot across Hart.
Mario Jelavic, a Croatia Under-19 international on trial with Roberto Mancini's squad, should have equalised but stabbed wide from close range, while Latics goalkeeper Alex Cisak was rooted to the spot when Milner flashed a 25-yard drive past the upright midway through the half.
Jelavic made a better fist of things in the 36th minute, clipping Nasri's 36th-minute pass against Cisak's near post.
The Australian keeper thwarted Milner twice either side of the interval, but could do nothing in the 53rd minute as Santa Cruz rounded him to score after a loose ball fell kindly.
Around the hour City's five returnees made way for a collection of youngsters including Slovakian playmaker Albert Rusnak, who drew two more excellent stops from Cisak before Grounds' late intervention.
"It was a good workout for the lads and our toughest pre-season game by far. We had to play a different type of game hitting them on the break," Dickov told the club's official website.
"We have to remember it is only a pre-season game and results don't count at this stage. But it is nice to win and I want us to get into the habit of winning and it becomes natural."
Dickov's men face one final test against Championship side Huddersfield at Boundary Park on Saturday before the new campaign begins.