High-flying Colchester dropped vital points as Oldham stormed back to earn a 2-2 draw at Boundary Park.
Marc Tierney's 56th-minute red card was the turning point as Oldham laid siege to the Colchester goal and over-hauled a two-goal deficit, equalising two minutes from time through teenager Ryan Brooke.
The visitors went ahead early when Oldham failed to clear a corner and David Fox drilled his shot inside the near post from 10 yards.
Both sides missed chances but the lead was doubled by Kayode Odejayi, who converted Anthony Wordsworth's free-kick with a deft header.
Ex-Oldham defender Tierney was sent off five minutes later when, having already been booked for a foul, he kicked the ball away in frustration at a decision.
And Oldham soon launched their fight back as Chris Taylor was dragged down by Magnus Okuonghae and picked himself up to convert from the spot.
Oldham, chasing only their third home win since February, took total control but could not make it count for another 25 minutes. Keigan Parker crossed from the right and fellow sub Brooke dived to head in from close range.
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