The Irish province travelled to Italy to face a Treviso side that had collected just one league point this season, while Leinster themselves had won four out of seven.
O'Connor's men were dealt a blow in the pre-game warm up when Luke Fitzgerald picked up an injury and had to be replaced by Brendan Macken, while hooker Richardt Strauss was also forced off at the break injured.
But Leinster struggled to find top gear throughout, and while pulling five points ahead with 12 minutes remaining through Darragh Fanning's converted try, they were again pegged back by the determined Italians.
Davide Giazzon crossed for Treviso to level the scores, before Jayden Hayward missed his conversion and then a penalty with three minutes left which would have handed his side the win.
Jimmy Gopperth did try and salvage an unlikely victory for Leinster with a drop-goal attempt with the final kick of the game but it flew wide, leaving O'Connor accepting his side had been below their best.
"It was disappointing. We let ourselves down. We didn't have a lot of ball in the second half and therefore couldn't manage enough territory or possession," he said.
"Luke complained of a tight groin after the warm-up and it wasn't worth taking the risk, while Richardt's hamstring tightened up and so we didn't want to take a chance with him either."
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