Motherwell tightened their grip on third position as they brushed aside the challenge of St Johnstone to move seven points clear of their hosts.
Omar Daley opened the scoring on the 16-minute mark when he tapped in Nicky Law's cross from the right.
The Fir Park team increased their advantage midway through the first half when Jamie Murphy headed Tom Hateley's centre past Peter Enckelman.
Murphy deflected Daley's 20-yard drive home to seal victory on 68 minutes.
The first chance came for the Lanarkshire side when Law was put through on goal by Michael Higdon, but he could only sweep a left-foot effort well wide from around eight yards.
St Johnstone responded immediately and a Carl Finnigan reverse pass found Murray Davidson in the penalty area, only for Darren Randolph to block the effort with his knees.
Steve Lomas' side kept up the pressure and Chris Millar floated a cross over from the right that was won in the air by Liam Craig. However, the ball was handled in a goalmouth scramble and the opportunity was lost.
Motherwell next made St Johnstone pay as they forged ahead through Daley. Law drilled a ball from the left across the six-yard box that neither Enckelman nor Callum Davidson could cut out and the winger converted from close range.
The home team tried to respond and a Craig cross from the left reached the head of Davidson, but the midfielder's header looped just wide.
Stuart McCall's men again showed a clinical edge to double their lead.
Daley was fouled by Davidson, but referee Alan Muir played advantage, Hateley swept in a cross from the right and Murphy's header beat Enckelman and nestled in the bottom left-hand corner of the net.
The Jamaican was in the mood and threatened again just before half-time.
He burst through the home defence and was brought down by the goalkeeper, but Muir ruled that the Finn had played the ball and gave a corner, with little complaints from the visitors.
St Johnstone were having plenty of possession in the early stages of the second half but failed to seriously test Randolph in the Motherwell goal.
However, that man Daley continued to be a danger and, on the hour mark, he danced into the penalty area and got a fierce shot away that Enckelman parried to safety.
He proved pivotal once again as Motherwell sealed victory with a third goal.
A short corner was relayed to the pacy forward 25 yards out and his shot deflected off Murphy and into the net.
The McDiarmid Park side launched a desperate final foray in the closing stages.
However, Motherwell coped comfortably with the best efforts of the home side and secured what could prove to be a crucial victory over their rivals.