Much-changed Celtic suffer St Johnstone defeat
Celtic, who made seven changes from Sunday's win over Aberdeen that clinched their fifth Scottish Premiership title in a row, took a 53rd-minute lead as Leigh Griffiths bagged his 40th goal of the season.
However, their lead was short-lived as Steven MacLean took advantage of a Stefan Johansen error to dink home a 56th-minute equaliser.
A misunderstanding between Celtic 'keeper Logan Bailly and defender Efe Ambrose then allowed Graham Cummins to restore St Johnstone's lead in the 77th minute which sealed their fourth straight victory and ended a 12-match unbeaten run for the Hoops.
Celtic assistant manager John Collins was philosophical in defeat.
"We were disappointed in the two goals that we lost but that's football," Collins said.
"We made a lot of changes tonight. The league is won so it was important to give all the boys a game."
Meanwhile, St Johnstone manager Tommy Wright was delighted to see his side seal fourth spot.
"There wasn't a lot of chances in the game but I thought we always looked a threat," Wright said.
"We did well after the split last year and we've done even better this year. Four wins on the bounce is incredible."
- Unrecognisable -
Celtic were almost unrecognisable from the match against Aberdeen on Sunday as manager Ronny Deila rung the changes for the match in Perth.
Ryan Christie was making a rare start and after a sluggish opening the winger created the first chance for the Glasgow giants.
The former Inverness Caledonian Thistle player danced his way to the by-line and swung a cross to the back post where Griffiths powered in a header that was beaten away by Zander Clark.
St Johnstone responded with a Liam Craig free-kick that reached Brian Easton at the back post but his shot was blocked by a team-mate.
Chris Kane then came close with an angled shot from the edge of the penalty error that fizzed narrowly wide of the post.
Patrick Roberts, who grabbed a double in the win over Aberdeen, then saw his shot from 20 yards take a deflection off a defender's boot and loop narrowly wide.
The Hoops took the lead shortly after the break as Griffiths became the first player since Swedish striker Henrik Larsson to reach 40 goals in a season for Celtic.
He gathered the ball on the left edge of the box following a quick breakaway and cut through three desperate challenges to coolly prod the ball past Clark with the outside of his boot.
However, St Johnstone soon found themselves on level terms through MacLean.
The striker robbed a dithering Johansen of possession in the box before dinking the ball over the head of the advancing Bailly.
Another defensive mistake from Celtic then allowed St Johnstone to take the lead.
JoeÂ Shaughnessy swung in a cross from the right and as Bailly grabbed the ball he collided with team-mate Ambrose, who headed the ball out his hands.
The loose ball fell to substitute Cummins, who had the simple task of firing home from close range.
The win confirmed that St Johnstone will finish fourth, with Motherwell fifth after Stephen Pearson scored twice in a 3-1 victory at Ross County.
Elsewhere, Danny Devine got the only goal as Inverness triumphed 1-0 at Hamilton and Kilmarnock came from behind to draw 1-1 at Dundee.
Relegated Dundee United drew 3-3 at home to Partick Thistle on Tuesday, while second-placed Aberdeen host Hearts on Thursday.