Match-winner Devante Cole bounced back from a miss of the season candidate to hoist Motherwell into third place.
The on-loan Wigan striker contrived to scoop a point-blank touch over the crossbar with the target at his mercy.
But Steelmen manager Stephen Robinson has hailed the 24-year-old centre-forward’s strength of character after he persevered to sink winless Saints with a tap-in two minutes before the interval.
It was his first league strike since moving north.
Robinson said: “Devante has shown his character. He had a couple of minutes feeling sorry for himself then got back to himself and scored the winner.
“Devante has had a great chance to score and showed character to react to his miss.
“I have missed one like that myself so I know what it is like. It might have been worse than his.”
Motherwell rode their luck when defender Scott Tanser became the latest St Johnstone player to squander a chance from the penalty spot shortly after the break, with Well goalkeeper Mark Gillespie brilliantly fending off the full-back’s effort.
Robinson, who is weighing up an appeal against midfielder Liam Donnelly’s dismissal for a stamp on Saints sub Chris Kane in the final seconds, acknowledged Well had ground out the points without being at their best.
“We were not on it and to win when not playing well showed our character,” he said.
“The penalty save was a huge turning point. Mark was outstanding all day and had another really good save.
“We won’t get carried away being up to third. There are massive aspects of the game we can improve on.”
Saints manager Tommy Wright, whose side remain stuck at the foot of the Ladbrokes Premiership table without a win in seven games, admitted it was an all-too-familiar story as the hosts missed chances and paid the price for defensive frailty.
“The goal we lost was horrendous. The penny isn’t dropping with some individuals, people are not doing their jobs when it matters,” he said.
Midfielder Murray Davidson should have scored with a late header and striker Stevie May was denied by Gillespie late in the game.
“We created a lot of chances and missed a penalty,” said Wright.
“There’s no doubt in my mind we should have won the game but you can’t gift teams goals the way we are.
“The worst we should have come out of the game with is 0-0. There’s no doubt we were the better side.
“Are Motherwell miles better than us? No, I don’t think so, but we gave away another poor goal and didn’t make enough of the good play we had.”