And Perth captain Jason Kerr has backed the repentant forward to repay his team-mates when he returns to the side.
O’Halloran left referee Kevin Clancy with no choice but to send him off when he caught Calum Butcher late in first half stoppage time.
By this point Saints were already a goal behind to Nicky Clark’s penalty.
Having previously been booked for a mistimed sliding tackle on Peter Pawlett and been given a last warning following a foul on keeper Benjamin Siegrist, O’Halloran made a huge error of judgment in committing a hat-trick of offences.
But the full-time dressing room apology has drawn a line under the episode and once he returns from suspension the former Rangers man will have an important part to play, according Kerr.
“It was disappointing for Mikey,” said the Saints skipper. “He had three fouls he could have been sent off for.
“He’s put his hand up, said he’s sorry and we’ll accept that.
“What I would say is he was going for the ball for all three fouls.
“We’ll not be too harsh on him. I’m sure he’ll dig us out of a hole later in the season. He’ll bounce back.”
A comeback draw against the Championship title winners, while a man light for over 45 minutes, was certainly a better way to get their league campaign going than last year’s 7-0 thrashing by Celtic.
Kerr said: “It was really important that we started well this time.
“Last season against Celtic was really poor – and it wasn’t just that match, it was the first nine games.
“Getting a draw, considering the circumstances, isn’t a bad result and hopefully we can build on it now.”
One of Saints’ best players was debutant Danny McNamara at right wing-back.
Kerr was very impressed with the on-loan Millwall man, who produced a brilliant last-ditch tackle to deny United a late winner.
He said: “Danny showed in the pre-season friendlies he’s a top player. The gaffer obviously worked with him at Millwall. The tackle at the end showed how good he is.
“It was a really good debut.”
Meanwhile, keeper Zander Clark missed out at Tannadice with a knee injury, manager Callum Davidson reported, but shouldn’t be sidelined for too long.