With Hearts losing away to Partick Thistle, the 2-0 McDiarmid Park defeat by Kilmarnock prevented St Johnstone from leapfrogging the Tynecastle side into fourth in the Premiership table.
Victory would also have moved them three points shy of Rangers, who they face at Ibrox on Wednesday.
Manager Tommy Wright had no complaints about the result but had plenty of criticism for his side’s performance.
He said: “It was a horrible first 45 minutes, which set the tone for us. They deserved to win but it was diabolical from us in the first 45. It was brutal and they’ll have to get over it.”
Tommy added: ““It was comical, and I’m sure it left a lot of fans numb because it certainly did myself..”
A brilliant early lob from Rory McKenzie and Conor Sammon’s second-half header earned the visitors just their second victory in their last 12 matches.
However, it was an afternoon to forget for Saints as they commemorated their 132nd anniversary.
Wright went on: “I can’t believe the first half and it’s probably the worst performance since I’ve been here and I’ve been here six years.
“The number of mistakes, non- tackles, not winning second balls, misplaced passes, players caught in possession. You have to give Killie credit but I’m looking to my team and we didn’t do the basics well.
“Someone said you know after a minute how your team will play but we knew after about 15 seconds.”