Michael Higdon's clinical hat-trick sent Motherwell level on points with second-placed Inverness in the Clydesdale Bank Premier League - but only after they repelled a late fightback.
Motherwell looked to be coasting when Higdon swept home his third goal in the 69th minute after two early goals.
But Nigel Hasselbaink and Liam Craig beat Lee Hollis within the space of two minutes just after the goalkeeper had replaced the injured Darren Randolph, setting up a nervy finish.
However, Hollis made an excellent late save from Hasselbaink to keep the three points at Fir Park.
Motherwell did not need new loan signing Kallum Higginbotham to maintain their European challenge following Jamie Murphy's move to Sheffield United.
Bob McHugh, who netted four goals in a midweek under-20s game against the Perth side, made his second start of the season up front alongside Higdon while Henrik Ojamaa was in left midfield.
St Johnstone were forced into one change after Murray Davidson picked up an ankle injury. Steven MacLean came in up front with Rowan Vine moving wide left and Liam Craig, who signed a pre-contract deal with Hibernian in midweek, playing in central midfield.
Both managers had placed the emphasis on attack in their team selections and the match started in open fashion before Higdon struck in the eighth minute.
The former Falkirk and St Mirren striker helped launch the move in his own half when he set Chris Humphrey free down the right wing after McHugh's flick.
Higdon was quick to support the winger and swept a wonderful first-time finish into the bottom corner from 16 yards after Humphrey had picked him out with a measured pass.
Home captain Keith Lasley cleared off the line after Craig's corner had glanced off the head of Motherwell defender Shaun Hutchinson and McCall's side moved two ahead in the 20th minute.
Ojamaa rolled the ball into Higdon who failed to connect properly with his first effort after turning Frazer Wright, but the ball broke back to him 14 yards out and he fired a shot low into the net.
St Johnstone dominated the rest of the half as Motherwell struggled to get out of their own half with Ojamaa unable to get on the ball.
But Hutchinson and Simon Ramsden defended strongly and Randolph twice made comfortable saves from the lively Vine.
Tade somehow headed against the post from a yard out but his embarrassment was partly saved as Vine's cross was wrongly ruled to have gone out of play first.
Vine's deflected cross bounced off the bar just after the break and MacLean delayed after being played through by Dave Mackay before shooting straight at Randolph.
But Motherwell had rediscovered their attacking drive at half-time and Higdon was on target again.
Hutchinson rose well to meet Tom Hateley's corner and his header broke off a defender to Higdon, who dispatched the ball into the corner from 10 yards.
Motherwell lost Randolph to what looked like a groin injury after MacLean had just failed to turn home Vine's low cross.
Hollis was soon picking the ball out of the net after substitute Hasselbaink played the ball into MacLean and ran on to his lay-off to curl high into the corner from 18 yards.
Saints soon set up an exciting finish in the 79th minutes when Craig fired a powerful first-time effort into the bottom corner from 20 yards after Mackay's cross had been half-cleared.
Hollis had little chance with either effort and he ensured the victory in the 89th minute when he rushed off his line to save from Hasselbaink after the Dutchman had forced his way beyond the home defence, although there was still time for Vine to volley over from close range after Mackay had robbed home substitute Zaine Francis-Angol.