Motherwell dished out a 3-1 come from behind defeat on champions Celtic on Sunday to guarantee the Fir Park side one of the Scottish Premier League's two Europa League qualifying spots next season.
Celtic, who made six changes from the side that clinched the title last weekend, took a 40th minute lead through Gary Hooper.
However, Motherwell were level seconds before the break when Henrik Ojamaa rifled a low shot beyond Fraser Forster.
The Estonian striker then earned his side a 50th minute penalty which Michael Higdon smashed past the keeper.
A bizarre own goal moved Motherwell further in front five minutes later when Hoops defender Mikel Lustig's header hit Forster's back after rebounding off the base of the post.
Victory earned Motherwell back-to-back wins over Celtic for the first time in 14 years and moves them nine points clear of third-placed Inverness Caledonian Thistle with three games remaining.
"I don't know where that result came from because I thought we totally dominated the first half," a bemused Celtic manager Neil Lennon said.
"For some reason we just didn't come out of the traps in the second half and we have given away a penalty and an own goal. I thought going forward we were very good but defensively we were poor."
His Motherwell counterpart Stuart McCall praised his side's performance.
"You can say they had people missing but they brought international players in as replacements and I just think our lads were outstanding," McCall said.
"I normally say you have to score the first goal to win a game against one of the Old Firm but they showed character to go behind and come back and put in a performance like that."
With several Celtic players being afforded a break following the clinching of their second successive SPL title, Tom Rogic was handed a rare start at Fir Park and teenage striker Tony Watt made the starting XI for the first time since December.
The pair combined for Celtic's first chance with just over a minute played. Australian international Rogic pinged a ball over the top of the Motherwell defence and Watt took a touch on his chest before firing a dipping shot just over the bar.
But for a little more composure Motherwell would have gone ahead in the 28th minute when James McFadden showed great skill to cut in from the left and jinked past three Celtic players but then sliced his shot wide.
A superb save from Darren Randolph denied Hooper in the 34th minute. Watt swung over a perfect cross from the left wing into the six-yard box where the ball dropped perfectly for Hooper, but his volley was blocked at point-blank range by Randolph.
Hooper did fire Celtic in front at the second attempt in the 40th minute. Watt's surging run brought him into the box and he dinked the ball over the advancing Randolph to Hooper, who headed his first effort off the bar but fired the rebound into the empty net.
Motherwell were level seconds before the break. Keith Lasley played a defence splitting pass through for Ojamaa to chase and the Estonian smacked a low left-foot shot past Forster at his near post from 20 yards out.
Ojamaa then earned his side a penalty in the 50th minute after Charlie Mulgrew clipped the heels of the striker in the box. Higdon stepped up and expertly dispatched his spot-kick into the top left-hand corner of the net for his 25th goal of the season.
Motherwell moved 3-1 in front in strange circumstances. Lustig, under pressure from Higdon, headed Hately's lofted pass off the post and it bounced out and hit off the back of Forster and into the net.