The home side had already been reduced to 10 men shortly before half-time with Calum Butcher receiving a straight red for a low blow on Dons striker Christian Ramirez.
Then just minutes later, Ojo's momentum took him into the stand where he was pushed in the chest by a home fan.
Referee Bobby Madden - who had booked Ojo earlier in the half - flashed a second yellow and then a red at the Aberdeen player, who had to be escorted down the tunnel as he was barracked by the United fans.
Glass was also given his marching orders when he remonstrated with the official in the tunnel at half-time.
United are set to review footage of the incident but the Dons manager was disappointed that Ojo's initial movement back towards the fan after being pushed gave Madden a decision to make with the home side taking all three points in the second half thanks to an Ian Harkes' goal.
Glass said: "It's disappointing as we were in control for the bulk of the game. More so when it went 10 v 11.
"Then a little bit of indiscipline from Funso going back to the incident probably cost us the chance in the second half to have an extra man.
"It shouldn't happen. He has hopped the boards after the ball has run out of play. He is pushed but goes back towards the incident.
"The referee could protect the player a little bit rather than produce a second yellow.
"I have not spoken to him (Ojo) and he looks disappointed.
"I will support the player although I do think he has let us down a little bit."
Glass also insisted he was only asking referee Madden for clarity when he was red carded.
He added: "I questioned a couple of his decisions - that was it. The referee decided I was questioning his integrity which I would never do."
Meanwhile, United head coach Tam Courts was delighted that his side had moved level on points with Hearts in third place in the Premiership table.
Courts said: "The longer the game went on I think one goal was always going to win it and thankfully it came for us through Ian Harkes."
Courts admitted he did not witness the incident where Butcher was sent off.
He added: "I didn't actually see it at the time. I tend not to dwell on these situations just because the decision has been taken and made."
It was a frantic clash between the north-east rivals with challenges flying in from both sides.
Ramirez had the best chance for the Dons in the first half but the American hit his low angled drive past United keeper Benjamin Siegrist's right-hand post.
United upped the pressure in the second half and home sub Louis Appere forced Joe Lewis to turn his shot onto the post and behind.
However, the Tangerines did finally break the deadlock in the 80th minute. Scott McMann swung a corner in from the left with the ball making its way to Harkes who produced a fine finish with the outside of his right foot to secure all three points for the home side.