For Oldham, a sixth defeat in seven starts heralds the spring with a fraught battle to stay in League One.
There was an edgy start with City needing to overturn the record book which showed them winning more points away than at home.
With just eight points from 11 games Oldham brought in Steve Mildenhall for his debut in goal in place of the Australian Les Pogliacomi. It was not a happy experience.
Oldham skipper Dean Holden was injured in the first minute and Mildenhall was left with next to no cover when Luke Wilkshire got in an eighth minute cross from the left. Tony Dinning headed it down and Leroy Lita buried it for the first of his two goals by the midway point of the first-half.
For his second, taking his total for the campaign to 23, the ball again came in from the left, although by this time Holden had gone off to be replaced by Kevin Betsy.
Lita cut back inside Will Haining and the finish was clinical, low into the far corner.
With Lita fired up and City stoking up the pressure with their crosses Stephen Brooker passed up the chance to kill off Oldham, lifting a free header over the bar.
Then for about a quarter of an hour the Lancashire side enjoyed their best spell. Chris Killen snapped in several shots, Wilkshire had to block an effort from Mark Hughes on the line and the corner that followed hung around dangerously.
Oldham worked hard for a goal that would have given them hope but luck was not with them and neither was a good defensive plan.
Right on half-time Mickey Bell tried to find Lita with a long ball. The bounce fell to Wilkshire, Guy Branston fell over and as Mildenhall came off his line Wilkshire was able to walk in the third goal.
Bristol had two teenagers in their line-up and 17-year-old David Cotterill, who had an enterprising night on the right, broke away early in the second-half and after going past two defenders, laid a pass back for Brooker to side-foot his season's 16th goal.
Will Haining pulled one back for Oldham with a free header from a corner, but this was always Bristol's night and Branston underlined it with a late own goal.