Motherwell consolidated their third-top place in the Scottish Premier League with a convincing win over a lacklustre St Johnstone.
Saints had started the brighter until a disputed 17th-minute penalty was dispatched by Michael Higdon.
Nicky Law added the second from close range three minutes later.
Jamie Murphy volleyed in seven minutes after the break, Liam Craig pulled one back with a 59th-minute penalty before Henrik Ojamaa's late breakaway double.
It means Motherwell stretch their lead over Dundee United to five points as they chase a place in next season's Champions League qualifiers.
The Perth side's plans were disrupted just before kick-off, with the influential Dave Mackay picking up an injury.
It meant a start for Steven Anderson in defence for a Perth side already without their lethal SAS partnership up front, with Francisco Sandaza suspended and Cillian Sheridan a surprise omission.
Marcus Haber was handed a lone striking role, with Craig and Jody Morris returning from suspension, while Jamie Adams dropped to the bench.
However, despite a drive from Murphy that curled just wide from 20 yards, St Johnstone edged the opening exchanges and Darren Randolph saved decent long-range efforts from David Robertson and Derek Riordan.
The match turned when Anderson was adjudged to have brought down Humphrey just inside the box.
Well's flying winger had evaded Craig's attempt to haul him down and Anderson slipped as he went to into his challenge.
Referee Bobby Madden decided that what looked like an accidental challenge had sufficiently impeded Humphrey and Higdon sent Alan Mannus the wrong way from the penalty spot.
Humphrey pounced on some hesitation from Morris three minutes later before delivering a ball across the face of goal for Law to slide home from close range.
Riordan curled a free-kick just wide moments later, but Saints were struggling to cope with Motherwell's attacks and Humphrey in particular.
The right winger drew an excellent one-handed save from Mannus, who held Murphy's follow-up.
Murphy then found space down the left before cutting inside to pass to Higdon, whose flicked effort on the stretch from 18 yards was touched just wide by Mannus.
Randolph saved another long-range Riordan strike and then came off his line quickly to block from David Robertson to maintain Motherwell's lead going into the break.
Murphy was making the most of being handed a start with Keith Lasley, who had returned from suspension, in place of Omar Daley and Stuart Carswell.
The forward superbly volleyed home a fine Tom Hateley cross after the break and perhaps should have done better than fire against the chest of goalkeeper Mannus minutes later.
Saints were handed a lifeline when Shaun Hutchinson hauled back Haber and Craig powered the resulting penalty past Darren Randolph.
The visitors were given new lease of life, but Well survived the pressure and, when Humphrey again broke clear, substitute Ojamaa slotted in with seven minutes remaining.
There was still time for another Ojamaa strike on the break to creep under Mannus and just over the line.
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Live Text Commentary
Full Time The match has reached full-time.86:37
Assist on the goal came from Darren Randolph.86:37 Goal scored
Goal! - Henrik Ojamaa - Motherwell 5 - 1 St J'stone Henrik Ojamaa finds the net with a goal from inside the penalty area to the bottom left corner of the goal. Motherwell 5-1 St Johnstone.85:01 Substitution
Substitution Ross Forbes is brought on as a substitute for Keith Lasley.85:01
Marcus Haber fouled by Tim Clancy, the ref awards a free kick. Derek Riordan produces a strike on goal direct from the free kick.84:35
Michael Higdon produces a left-footed shot from inside the area that clears the crossbar.84:10
Nicky Law restarts play with the free kick.84:10 Booking
Booking Alan Maybury receives a yellow card for unsporting behaviour.83:58
Free kick awarded for an unfair challenge on Henrik Ojamaa by Alan Maybury.82:48
Assist on the goal came from Chris Humphrey.82:48 Goal scored
Goal! - Henrik Ojamaa - Motherwell 4 - 1 St J'stone Henrik Ojamaa fires in a goal from inside the penalty area to the bottom left corner of the goal. Motherwell 4-1 St Johnstone.81:18
Free kick awarded for a foul by Alan Maybury on Michael Higdon. Stevie Hammell takes the direct free kick.79:54 Substitution
Substitution Stewart Carswell on for Steve Jennings.79:54 Substitution
Substitution Henrik Ojamaa is brought on as a substitute for Jamie Murphy.79:54
Unfair challenge on Tim Clancy by Marcus Haber results in a free kick. Darren Randolph takes the free kick.77:30
Jack Compton has a volleyed shot. Save by Darren Randolph.74:58 Substitution
Substitution Liam Craig goes off and James Keatings comes on.69:49
Michael Higdon is ruled offside. Alan Mannus restarts play with the free kick.68:04
Alan Maybury challenges Nicky Law unfairly and gives away a free kick. Darren Randolph restarts play with the free kick.66:31
Tim Clancy takes the free kick.
Booking Murray Davidson receives a caution.66:25
Murray Davidson gives away a free kick for an unfair challenge on Steve Jennings.65:40
Free kick awarded for an unfair challenge on Shaun Hutchinson by Derek Riordan. Direct free kick taken by Darren Randolph.64:10
Marcus Haber is ruled offside. Darren Randolph takes the indirect free kick.63:45
Jamie Murphy takes a shot. Alan Mannus makes a save.63:28
Shot by Michael Higdon. Save by Alan Mannus.62:04
Corner taken by Tom Hateley, comfortable save by Alan Mannus.61:31
Free kick awarded for a foul by Marcus Haber on Tim Clancy. Direct free kick taken by Darren Randolph.60:23
Alan Maybury fouled by Nicky Law, the ref awards a free kick. Alan Mannus restarts play with the free kick.59:21
Tim Clancy concedes a free kick for a foul on Marcus Haber. Liam Craig restarts play with the free kick.58:50 Goal scored
Goal! - Liam Craig - Motherwell 3 - 1 St J'stone Power penalty scored by Liam Craig. Motherwell 3-1 St Johnstone.58:06
Marcus Haber fouled by Shaun Hutchinson, the ref awards a Penalty.56:26
Corner from the right by-line taken by Tom Hateley, clearance by Liam Craig.54:59
Jamie Murphy has a lobbed shot. Save made by Alan Mannus.53:44
Tom Hateley challenges Liam Craig unfairly and gives away a free kick. Direct effort from the free kick comes in from Liam Craig, save by Darren Randolph.53:00 Substitution
Substitution Jack Compton replaces David Robertson.53:00
The official flags Jamie Murphy offside. Alan Mannus takes the indirect free kick.51:28
The assist for the goal came from Tom Hateley.51:28 Goal scored
Goal! - Jamie Murphy - Motherwell 3 - 0 St J'stone Jamie Murphy fires in a goal from inside the area to the bottom left corner of the goal. Motherwell 3-0 St Johnstone.50:23
Nicky Law is flagged offside by the assistant referee. Alan Mannus takes the indirect free kick.49:12
Outswinging corner taken from the right by-line by Tom Hateley.47:45
The offside flag is raised against Jamie Murphy. Alan Mannus takes the indirect free kick.46:27
Michael Higdon fouled by David McCracken, the ref awards a free kick. Stevie Hammell takes the free kick.45:01
The second half begins.45:00 +1:05 Half time
Half Time It is the end of the first-half.44:18
Header from close range by Marcus Haber misses to the right of the target.43:32
Unfair challenge on Alan Maybury by Michael Higdon results in a free kick. Direct free kick taken by David Robertson.42:22
Effort on goal by David Robertson from 18 yards. Save by Darren Randolph. Corner taken left-footed by Liam Craig from the right by-line to the near post, Steve Jennings makes a clearance.40:18
Inswinging corner taken by Tom Hateley from the left by-line played to the near post, clearance made by Alan Maybury.39:57
Free kick awarded for an unfair challenge on Stevie Hammell by David Robertson. Nicky Law takes the free kick.38:43
Outswinging corner taken right-footed by Tom Hateley from the right by-line.37:30
Keith Lasley concedes a free kick for a foul on Murray Davidson. Direct free kick taken by Steven Anderson.36:24
Unfair challenge on Shaun Hutchinson by Marcus Haber results in a free kick. Darren Randolph takes the direct free kick.33:52
Derek Riordan has an effort at goal from 25 yards. Comfortable save by Darren Randolph.32:40
Michael Higdon takes the chance to get an effort at goal. Save by Alan Mannus. Tom Hateley takes a corner.28:36
The official flags Jamie Murphy offside. Alan Mannus takes the indirect free kick.27:50
Drilled right-footed shot by Chris Humphrey. Alan Mannus makes a save. Jamie Murphy takes a shot. Save made by Alan Mannus.27:05
Foul by Keith Lasley on David Robertson, free kick awarded. Alan Mannus takes the free kick.26:35
Outswinging corner taken by Tom Hateley from the right by-line, Steven Anderson manages to make a clearance.25:02
Michael Higdon challenges David McCracken unfairly and gives away a free kick. Alan Mannus restarts play with the free kick.24:13
Michael Higdon concedes a free kick for a foul on David Robertson. Free kick taken by Alan Maybury.22:06
Free kick awarded for a foul by Frazer Wright on Michael Higdon. Free kick taken by Nicky Law.20:36
Shaun Hutchinson concedes a free kick for a foul on Marcus Haber. Strike comes in from Derek Riordan from the free kick.19:31
Chris Humphrey provided the assist for the goal.19:31 Goal scored
Goal! - Nicky Law - Motherwell 2 - 0 St J'stone Goal scored by Nicky Law from close in low into the middle of the goal. Motherwell 2-0 St Johnstone.17:46
Michael Higdon concedes a free kick for a foul on Steven Anderson. Liam Craig takes the direct free kick.16:33 Goal scored
Goal! - Michael Higdon - Motherwell 1 - 0 St J'stone Penalty taken right-footed by Michael Higdon and scored. Motherwell 1-0 St Johnstone.15:53 Booking
Booking Steven Anderson booked for unsporting behaviour.15:31
Steven Anderson challenges Chris Humphrey unfairly and gives away a Penalty.14:48
Free kick awarded for an unfair challenge on Marcus Haber by Shaun Hutchinson. Free kick crossed right-footed by Derek Riordan from left wing, Steve Jennings makes a clearance.14:09
Free kick awarded for an unfair challenge on Steve Jennings by Murray Davidson. Stevie Hammell restarts play with the free kick.13:25
Liam Craig is adjudged to have handled the ball. Direct free kick taken by Shaun Hutchinson.12:36
Jamie Murphy produces a left-footed shot from just outside the area that goes wide left of the goal.11:55
The referee blows for offside. Darren Randolph restarts play with the free kick.10:56
Derek Riordan has an effort at goal. Darren Randolph makes a save. Inswinging corner taken by Liam Craig from the right by-line played to the near post.10:11
Steven Anderson has a volleyed shot. Save made by Darren Randolph.9:02
Chris Humphrey fouled by Steven Anderson, the ref awards a free kick. Tom Hateley restarts play with the free kick.6:44
Jamie Murphy is flagged offside by the assistant referee. Alan Mannus takes the indirect free kick.6:17
Foul by Frazer Wright on Michael Higdon, free kick awarded. Keith Lasley takes the direct free kick.5:45
Tom Hateley fouled by Liam Craig, the ref awards a free kick. Shaun Hutchinson takes the free kick. The official flags Jamie Murphy offside. Alan Maybury takes the indirect free kick.5:04
Jamie Murphy has an effort at goal from just outside the box which goes wide of the right-hand upright.4:12
Shot from just outside the box by Murray Davidson goes over the bar.0:00
The game begins.
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