Ten-man Wanderers snatched an equaliser in the 96th minute when Leon Johnson headed home from five yards after they had Josh Scowen sent off midway through the second half for two yellow cards within five minutes.
Ainsworth said: "We were the better side in the second half and as soon as Josh went off it gave them a chance to kill it off, but we did well and Leon Johnson was in the right place at the right time.
"It's a nice feeling to be on the right end of late goals this season but I was very disappointed with Josh. I've had a right go at him. It's immature and reckless.
"I'm angry, but very relieved. Scunthorpe will feel hard done by that they couldn't kill it off but we threw everything at them and deserved the goal.
"I thought there were a few handballs in the first half not given for us but if there is one at the end I didn't see it - but my assistant tells me it definitely was.
"If we've got one there then it isn't nice for the opposition manager, but we've got to take them."
- Sports & Recreation
- Josh Scowen
- Deon Burton