The Hoops boss gave rare starts to stand-in keeper Lukasz Zaluska, and forwards Teemu Pukki, Derk Boerrigter and Amido Balde but felt his side were "disjointed" in the first-half.
Defender Tim Clancy gave the home side the lead in the eighth minute before Saints' top scorer Stevie May had a penalty saved by Zaluska three minutes from the interval.
Kris Commons, on for Boerrigter for the start of the second-half, levelled from the spot in the 53rd minute after fellow substitute Scott Brown had been tripped by Gary McDonald.
Pukki and defender Virgil van Dijk added further goals, which looked to have the champions on easy street, but goals from midfielder Brown in the 83rd minute and Michael O'Halloran two minutes later left the champions on 96 points with a home game against Dundee United Sunday left in the campaign.
Asked if he felt frustrated at missing out on the century target, the Hoops boss said: "Not really. You set yourself little targets and it would have been a nice milestone and we should have done because we were 3-1 up with 10 minutes to go, but we have scored 99 goals, we are one short for 100 and that would be nice to finish the season off with that.
"I am really looking forward to Sunday. The lads haven't had the opportunity to celebrate the title win so to get the trophy at home will be a special day and I want them to finish the season on a high.
'It was a game of two halves tonight. We were poor in the first half but very good in the second.
'We threw away two goals at the end which is disappointing but we made the changes because we wanted to give some players a game. There was a disjointed look about us in the first half - we didn't play well at all.
'We decided to make the changes at half-time but having said that over the piece a draw was a fair result."
The former Celtic skipper admitted he made his feelings known at the interval.
He said: 'Yes. I did. It was unacceptable. We were miles off the level we've been at. And I'm not just talking about the players that came in either. Some of the players who were playing on a regular basis weren't at it.
"I wasn't happy with our defending for the final two goals either. I thought we were lazy.
"There was a fluency about us in the second half which missing in the first half.
"I will take responsibility for that because I made the changes because I wanted to. I wanted to give players an opportunity to play.
'But I can't be too critical of my players. Since we won the league they've kept their momentum going."
Saints boss Tommy Wright replaced May with Nigel Hasselbaink at the interval after he took a knock in the first-half when challenged by Efe Ambrose, but he insisted he had no worries over his top scorer and simply had an eye on the William Hill Scottish Cup final against Dundee United a week on Saturday.
He said: "Stevie's fine. The plan was to give him only 60 minutes anyway. He took a nasty one, stud marks on his shin, but there's no problem with it at all. It was just precaution he came off."
The Northern Irishman added: "I was delighted with the performance. We deserved a point.
"Other than the penalty miss we had other opportunities to be more than just one ahead.
"We had a lot of excellent performers like O'Halloran and Paddy Cregg while young Scott Brown was also superb."