Oldham raced to their first win of the season as Walsall lost a two-goal lead for the second time in a week.
The Saddlers did not learn that lesson ,after been pulled back for a draw in midweek and they were heavily punished by the five-star Latics at Boundary Park.
Oldham were on top in the early stages, but both teams had their chances as poor defending set the tone for the afternoon.
Walsall made one count after 29 minutes when Matt Fryatt made the most of mistake by home goalkeeper Les Pogliacomi and placed the ball past him from 18 yards.
Walsall doubled their lead five minutes later when a short corner was played to Daryl Taylor who smashed an unstoppable shot into the far corner from a difficult angle.
But Oldham began their fightback before half-time as veteran David Eyres began to steal the show at the age of 40.
Eyres converted a free-kick from 22 yards by beating the visiting keeper at his near post and he followed up with a powerful shot from the edge of the penalty area with took a slight deflection on its way in.
Oldham captain Dean Holden scored after 50 minutes as his drive from 20 yards was badly handled by Walsall keeper Richard McKinney, who was the subject of criticism from his manager after the game.
Rchard McKinney got a touch to the fourth, but he could not save the close-range effort from the Rodney Jack after a good cross from Jermaine Johnson.
Fryatt was felled in the penalty box and got up to score from the spot with 13 minutes left as Walsall tried to beat back, but Oldham killed them off in injury time, with a sweet finish by Adam Griffin from 20 yards.