Murphy bullets a header into the far corner for Motherwell's opener
St Mirren's relegation fears worsened as Motherwell recorded a convincing Scottish Premier League win in Paisley.
Jamie Murphy nodded the visitors in front from Steven Hammell's cross before David Clarkson doubled Well's lead before half-time.
Clarkson headed Motherwell's third on the hour mark and came close to a hat-trick with left-foot shot.
Stephen O'Donnell pulled one back for St Mirren but it proved to be no more than a consolation strike.
The result means St Mirren now sit two points clear of SPL bottom club Falkirk, who drew with Kilmarnock.
The Buddies threatened first when Andy Dorman raced onto Billy Mehmet's flick and was prevented from finding the net by the alert goalkeeping of Graeme Smith, with Brian McLean clearing Stephen McGinn's rebound attempt.
And it was Motherwell who went in front through Murphy's third goal of the season on 18 minutes.
The home side cleared Jim O'Brien's corner but the ball was eventually played back into the box by Hammell and the unmarked Murphy planted a header into the back of the net.
Graeme Smith saved comfortably from Mehmet's shot and John Potter headed narrowly wide for before Motherwell grabbed a second goal in the 32nd minute.
Cillian Sheridan's cross was cushioned into the path of Stephen Hughes by Clarkson, who converted the rebound after the midfielder's shot had struck the post.
Clarkson celebrates the first of his two goals
Saints looked to reduce the deficit before half-time but David Barron's deflected shot was off-target.
Keeper Mark Howard's save prevented Sheridan from turning into the net as Motherwell continued to expose their hosts' defensive frailty.
A series of St Mirren set pieces at the beginning of the second half failed to yield a meaningful opening and Clarkson put the result beyond doubt with a well-taken third.
Hughes retained possession under pressure and released Paul Quinn, whose cross was despatched into the net by Motherwell's top scorer.
Clarkson blasted wide as he pursued a hat-trick with St Mirren again finding themselves under pressure.
O'Donnell lashed home from fellow substitute Garry Brady's cross to reduce the deficit with 18 minutes remaining.
St Mirren rallied and pinned their visitors back in the closing stages with Graeme Smith saving from Dorman and Steven Thomson.
But Motherwell survived the onslaught to see out the win and O'Brien missed the target from a promising position late on.
St Mirren manager Gus MacPherson: "I'm extremely disappointed. As soon as we lost the first goal, you could just see the effect that that had on the team. It was very, very poor defending.
"We went 3-0 down and I feared the worst and after that we did react but that's far, far too late.
"The last two games have been massive games for us and we've failed in them but we still find ourselves two points ahead of Falkirk.
"We would liked to have stretched that lead today but that's not happened.
"We've got two away games now which will be extremely tough games and we have to regroup, gather our composure and try and get a result out of that."
Motherwell manager Mark McGhee: "We played a fresher system and played a couple of young boys. We had a lot more energy and I thought we were thoroughly worthy of our victory.
"The way we passed the ball was the difference between the two teams. We moved the ball quickly with some good sequences of passing.
"We could've had a couple of more goals and we finished well when we got the chance. There was a lot good about our game today.
"These games are difficult because there's nothing at stake for us so, equally, I'm not going to start making a big scene just because we won one of them."
St Mirren: Howard, Ross (Haining 46), Potter, Cuthbert, Barron, Thomson, Murray, Dorman, McGinn (O'Donnell 62), Wyness (Brady 63), Mehmet. Subs Not Used: Mathers, Mason, McAusland, Camara.
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