Celtic celebrated the presentation of the Scottish Premier League trophy by delivering a blow to St Johnstone's Europa League qualification hopes.
It was a stroll at Celtic Park from the first minute, when Joe Ledley fired powerfully into the far corner.
Anthony Stokes claimed he had got a touch on a Charlie Mulgrew free-kick that curled in at the back post.
After the break, James Forrest drilled low into the far corner and Frazer Wright added a late own-goal.
Before kick-off, manager Neil Lennon had again failed to rule out a move to Everton to fill the vacancy created by his fellow Celtic old boy David Moyes' summer switch to Manchester United.
But the fact Lennon's team could swat aside the challenge of fourth-top Saints without reaching the heights of their own capabilities might not have done much for his chances of landing the Everton job should he want it.
Brown (right) was back in the Celtic line-up after three months out through injury
This was a victory as emphatic as the 16-point gap it opened up between Celtic and second-placed Motherwell pending the afternoon fixtures and gave ammunition to those who argue the SPL is not the sternest test of the Northern Irishman's abilities.
Countryman Steve Lomas and his St Johnstone side had travelled from Perth in confident mood, looking to extend their unbeaten run to seven games.
They also arrived unbeaten in the previous three SPL meetings between the sides this season.
However, with the exception of stomach-bug victim Kris Commons, Celtic were back to near full strength after recent time off for some before their Scottish Cup final against Hibernian.
Perhaps the most significant return was that of captain Scott Brown after a three-month absence and an early characteristic thrust into the opposing penalty box by the Scotland midfielder started the move that led to the opening goal.
It followed a brief Saints foray up to the other end of the park and there also were hints of a handball by Gary Hooper in the build-up.
Ledley took full advantage of anything missed by the officials to power a drive into the far corner of the net after Forrest had played it across the edge of the penalty box.
Saints goalkeeper Alan Mannus had scooped a Mikael Lustig shot clear at full stretch by the time Celtic extended their lead after 36 minutes.
Mulgrew swept in a trademark free-kick that deceived Mannus as it curled across a forest of brows and into the unguarded net at the back post.
If Stokes was right to claim the goal, it could only have been courtesy of a couple of split ends on the top of the Irish striker's skull.
Hibs-bound Liam Craig, who started in midfield ahead of the injured Chris Millar, should have pulled one back shortly after the break but volleyed a Steven McLean cross wildly over at the back post.
However, Forrest killed the game as a contest six minutes into the second half when he fired a 16-yard drive low into the far corner after being sent free by Gary Hooper on the break.
Forrest missed a great chance for his second when he blasted over from 14 yards, while Georgios Samaras also volleyed narrowly wide from close range.
Saints substitute Nigel Hasselbaink finally forced Celtic goalkeeper Frazer Forster into a save after 77 minutes, but it was a momentarily lapse for the comfortable Celtic defence.
The champions finally added to their tally when Wright powerfully headed a Mulgrew corner in the wrong direction and into his own net.
Saints' defeat - one goal short of the drubbing they received at Celtic Park in the Scottish Communities League Cup - leaves the Perth side a point behind Inverness Caledonian Thistle, who could now clinch the remaining European spot with victory over Dundee United.
Full Time The referee signals the end of the game.
The assist for the goal came from Charlie Mulgrew.
90:00 +0:23 Goal scored
Goal! - Frazer Wright - Celtic 4 - 0 St J'stone Frazer Wright concedes an own goal. Celtic 4-0 St Johnstone.
Inswinging corner taken left-footed by Charlie Mulgrew,
Nigel Hasselbaink fouled by Victor Wanyama, the ref awards a free kick. Free kick crossed right-footed by Liam Caddis from right wing, clearance by Victor Wanyama.
Headed effort on goal by Gary Hooper from inside the penalty box misses to the right of the target.
Substitution Emilio Izaguirre leaves the field to be replaced by Beram Kayal.
Booking Booking for Mikael Lustig for dissent.
A cross is delivered by Liam Craig, Joe Ledley makes a clearance. Corner taken right-footed by Liam Craig, Joe Ledley makes a clearance.
Inswinging corner taken left-footed by Liam Craig, Charlie Mulgrew manages to make a clearance.
Georgios Samaras sends in a cross, blocked by Liam Craig.
The referee blows for offside against Gregory Tade. Fraser Forster restarts play with the free kick.
Substitution Steven MacLean leaves the field to be replaced by Liam Caddis.
Free kick taken by Victor Wanyama.
Booking Patrick Cregg is booked.
Patrick Cregg gives away a free kick for an unfair challenge on Joe Ledley.
Substitution Dylan McGeouch is brought on as a substitute for James Forrest.
Callum Davidson takes the direct free kick.
Booking The referee shows Georgios Samaras a yellow card for unsporting behaviour.
Georgios Samaras challenges Liam Craig unfairly and gives away a free kick.
Centre by Emilio Izaguirre, Close range effort by Georgios Samaras misses to the left of the target.
Effort on goal by Georgios Samaras from just outside the penalty area goes harmlessly over the target.
Nigel Hasselbaink crosses the ball, Kelvin Wilson manages to make a clearance.
Steven MacLean crosses the ball.
Free kick taken by Charlie Mulgrew.
Booking Booking for Murray Davidson for unsporting behaviour.
Murray Davidson fouled by Anthony Stokes, the ref awards a free kick. Direct free kick taken by Liam Craig. Free kick awarded for an unfair challenge on Emilio Izaguirre by Murray Davidson.
Charlie Mulgrew produces a shot on goal direct from the free kick.
Substitution Nigel Hasselbaink joins the action as a substitute, replacing Rowan Vine.
Substitution Georgios Samaras comes on in place of Scott Brown.
Liam Craig gives away a free kick for an unfair challenge on Anthony Stokes.
Mikael Lustig restarts play with the free kick.
Substitution Thomas Scobbie goes off and Callum Davidson comes on.
Murray Davidson challenges Joe Ledley unfairly and gives away a free kick.
Inswinging corner taken left-footed by Liam Craig, Gregory Tade gives away a free kick for an unfair challenge on Victor Wanyama. Fraser Forster restarts play with the free kick.
James Forrest produces a right-footed shot from inside the area that goes over the bar.
Scott Brown gives away a free kick for an unfair challenge on Gregory Tade. Liam Craig crosses the ball in from the free kick, clearance by Scott Brown.
Scott Brown challenges Liam Craig unfairly and gives away a free kick. Alan Mannus takes the direct free kick.
The offside flag is raised against Anthony Stokes. Alan Mannus restarts play with the free kick.
Gary Hooper provided the assist for the goal.
51:00 Goal scored
Goal! - James Forrest - Celtic 3 - 0 St J'stone James Forrest finds the net with a goal from inside the area to the bottom left corner of the goal. Celtic 3-0 St Johnstone.
Booking Rowan Vine goes into the book.
Booking Victor Wanyama is shown a yellow card.
Steven MacLean sends in a cross, Shot by Liam Craig from just outside the area goes over the net.
The second half has started.
45:00 +1:30 Half time
Half Time The whistle is blown to end the first half.
Charlie Mulgrew gives away a free kick for an unfair challenge on Steven MacLean. Free kick taken by David MacKay.
Emilio Izaguirre takes a shot. Save made by Alan Mannus.
The ball is swung over by Emilio Izaguirre, clearance made by Frazer Wright. Inswinging corner taken from the left by-line by Charlie Mulgrew, Frazer Wright makes a clearance.
Emilio Izaguirre crosses the ball, clearance made by Steven Anderson.
James Forrest takes a shot. Save by Alan Mannus. James Forrest takes a short corner. James Forrest produces a cross.
Unfair challenge on James Forrest by Murray Davidson results in a free kick. Direct free kick taken by James Forrest.
Assist on the goal came from Scott Brown.
35:19 Goal scored
Goal! - Charlie Mulgrew - Celtic 2 - 0 St J'stone Charlie Mulgrew finds the net with a shot from the free kick. Celtic 2-0 St Johnstone.
Foul by Gregory Tade on Scott Brown, free kick awarded.
Scott Brown takes a shot. Blocked by Frazer Wright.
A cross is delivered by Emilio Izaguirre.
Joe Ledley sends in a cross, drilled right-footed shot by Mikael Lustig. Alan Mannus makes a save.
Inswinging corner taken right-footed by Charlie Mulgrew from the right by-line, clearance by Murray Davidson.
Unfair challenge on Patrick Cregg by Scott Brown results in a free kick. Free kick taken by Frazer Wright.
The ball is crossed by Emilio Izaguirre.
The ball is crossed by Gary Hooper, Anthony Stokes has an effort at goal from just inside the box that misses to the right of the goal.
Murray Davidson concedes a free kick for a foul on Gary Hooper. Free kick crossed left-footed by Charlie Mulgrew, Thomas Scobbie manages to make a clearance.
Liam Craig gives away a free kick for an unfair challenge on Anthony Stokes. Emilio Izaguirre takes the direct free kick. The ball is delivered by James Forrest, Patrick Cregg makes a clearance. Outswinging corner taken by Charlie Mulgrew, Rowan Vine manages to make a clearance.
Free kick awarded for an unfair challenge on Gregory Tade by Victor Wanyama. Rowan Vine crosses the ball from the free kick right-footed from left channel, clearance by Victor Wanyama.
The ball is sent over by Emilio Izaguirre.
The ball is sent over by Emilio Izaguirre, clearance by David MacKay.
Direct free kick taken by Mikael Lustig.
Booking Frazer Wright is shown a yellow card for unsporting behaviour.
Frazer Wright challenges James Forrest unfairly and gives away a free kick.
Direct free kick taken by Thomas Scobbie.
Booking The referee shows James Forrest a yellow card for unsporting behaviour.
Gregory Tade fouled by James Forrest, the ref awards a free kick.
Victor Wanyama takes a shot. Steven Anderson gets a block in.
The ball is sent over by Charlie Mulgrew.
The ball is crossed by Emilio Izaguirre, blocked by David MacKay. Corner taken left-footed by Charlie Mulgrew from the left by-line, David MacKay makes a clearance.
Unfair challenge on Emilio Izaguirre by Rowan Vine results in a free kick. Free kick taken by Emilio Izaguirre.
Victor Wanyama crosses the ball, clearance by Steven Anderson.
Mikael Lustig crosses the ball, clearance by Frazer Wright.
Headed effort from deep inside the penalty area by Mikael Lustig misses to the right of the target.
Steven MacLean gives away a free kick for an unfair challenge on Victor Wanyama. Charlie Mulgrew takes the free kick.
Liam Craig fouled by Victor Wanyama, the ref awards a free kick. Free kick taken by Alan Mannus.
Corner taken by Charlie Mulgrew, clearance by Patrick Cregg.
Assist on the goal came from James Forrest.
1:02 Goal scored
Goal! - Joe Ledley - Celtic 1 - 0 St J'stone Joe Ledley finds the net with a goal from just outside the area to the bottom right corner of the goal. Celtic 1-0 St Johnstone.
The ball is delivered by Steven MacLean, clearance by Mikael Lustig.
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