Kevin van Veen scored for the eighth consecutive game as Motherwell moved into seventh place in the cinch Premiership and left St Johnstone in relegation peril.
The Dutchman dinked home a re-taken penalty in the 52nd minute at McDiarmid Park after having his initial effort saved.
Motherwell survived a brief spell of late pressure before Mikael Mandron’s stoppage-time goal sealed a 2-0 victory which removes any lingering doubt about the Lanarkshire side’s top-flight status.
Van Veen has scored 11 goals in eight matches and 26 in total this season, while his 22-goal Premiership haul leaves him just two short of fellow PFA Scotland player of the year nominee Kyogo Furuhashi.
The only concern for the visiting support was the sight of the forward limping slightly with an apparent foot knock after being taken off late on.
Saints could not manage any shots on target and are only three points ahead of 11th spot with three games left and five ahead of bottom club Dundee United after Steven MacLean suffered his first defeat in three matches as interim boss.
Both sides made one change because of the absence of St Johnstone midfielder Melker Hallberg and Motherwell wing-back Max Johnston. Former Well attacker Jamie Murphy and Stephen O’Donnell came in.
There was little in the way of first-half action but Van Veen was at the centre of it. The Dutchman shot not far over from 22 yards with his left foot and had a goal disallowed for offside.
Motherwell’s Dan Casey had the only shot on target in the first half while Saints midfielder Graham Carey twice shot over the bar from half chances.
The breakthrough came out of the blue as Andy Considine tried to nip in front of O’Donnell just inside the box after Van Veen had helped the ball on. The wing-back got his body in the way and referee Grant Irvine pointed to the spot as soon as the Motherwell player went down.
Remi Matthews saved Van Veen’s initial spot-kick but referee Irvine quickly signalled a VAR check and soon pointed to the spot again for an encroachment.
Matthews dived the same way but his time Van Veen chipped down the middle of the goal.
The Dutchman soon threatened again after being left one-on-one with Considine but Matthews held his stabbed effort.
Stevie May and Drey Wright were off target from two decent openings for Saints, who lost Considine following a collision with Matthews.
Interim manager Steven MacLean brought on Chris Kane in the 84th minute as the striker made his first appearance since January 2022 and St Johnstone forced some corners but could not capitalise.
The win was wrapped up in the third minute of added time when Mandron finished from six yards after getting the ball back from Blair Spittal’s low cross.
St Johnstone are away to Kilmarnock in their next Scottish Premiership match on May 20, and Motherwell host Ross County.
Both games kick-off at 3pm.