Aberdeen were confident of claiming consecutive SPL wins for the first time under Mark McGhee and had the majority of possession at St Mirren Park.
But, with Lee Miller suspended and Darren Mackie up front alone, they lacked a cutting edge and Saints defender Chris Innes made them pay when his half-volley found the top corner from a 74th-minute corner.
The defeat, which followed an SPL win at Dundee United and Active Nation Scottish Cup triumph over Hearts, leaves sixth-placed Aberdeen just a point ahead of St Mirren and Motherwell.
"We can't keep on taking a defeat for us to react," Dons keeper Jamie Langfield told RedTV.
"We should be coming to places like this and going up the road quite easily with the three points.
"That would have given us a good platform to get up the table and catch up the likes of Dundee United. It's an opportunity missed.
"Now we have St Johnstone on Saturday, it's a massive game because they are just behind us.
"We need to go there and get three points and make sure we're climbing this league rather than going the other way."
Langfield made a point-blank save from Andy Dorman after three minutes but he otherwise felt comfortable until Innes struck.
"It's very frustrating," the 30-year-old said. "I don't think St Mirren contributed much to the game.
"I think they had two corners, and I had one save in the first half. Everything was played in their half and to get nothing was incredibly harsh on us.
"It's so frustrating coming off the back of two great wins. We were confident and played some good stuff and I can't believe we came away with nothing. It was a bit of a smash and grab.
"We felt so comfortable and Chris Innes just swung a leg at a corner and it's in the back of the net.
"Some people say it's a great finish but from our point of view he shouldn't be getting that space in the box.
"At the worst we should be coming away 0-0. We should be able to beat St Mirren, we maybe just need that wee ruthless streak."
McGhee admitted the defeat further highlighted his need for new strikers as he awaits answers from loan targets Steven MacLean and Stephen Dobbie.
But he is closer to persuading Charlie Mulgrew, who deputised in central defence in Paisley, to sign a new contract.
Aberdeen 6/4, St. Johnstone 7/4, Draw 12/5
Source: Team Talk
Source: Team Talk