Stephen Bradley says the sending off of Justin Ferizaj "completely changed" their game with Gent at Tallaght as the Hoops picked up a second Conference League point on Thursday night.
The hosts led the game for over 70 minutes after Rory Gaffney's early header but they were reduced to 10 men after Ferizaj was shown a second yellow card, and conceded an equaliser shortly afterwards.
From there, they were under huge pressure on the week their 20th SSE Airtricity League title was confirmed.
They will finish the group next Thursday in Sweden against already-qualified Djurgardens but Bradley believes a chance was missed for a victory - and the €500,000 that goes with it - in west Dublin.
"We came off the game 10 minutes before half-time and allowed them to dictate the game," the Hoops manager said afterwards.
"We stopped pressing, and they're a good team when you stop pressing and they hurt us a little bit. The second half we started ok again.
"The sending off, and the goal within two minutes, completely changed the game. That was frustrating because we were just about to take Justin off, because we knew he was on the edge.
"Literally he made the tackle and then within 90 seconds they score, so within two minutes we've given up a man and the goal.
"It's something we definitely have to learn from, going forward."
Bradley was forced to bring on 17-year-old Ferizaj earlier than he had intended after Dylan Watts and Chris McCann were both injured inside 35 minutes.
It added to the absences of Jack Byrne and Gary O'Neill, who were both unavailable for selection on the night.
"He's young, and he'll learn from that experience," Bradley said of Ferizaj's two yellow cards.
"If we keep 11 on the pitch we've every chance of scoring that second
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