Manchester City suffered a shock defeat as their seemingly inevitable march to the Premier League title hit a bump in the road with a last-gasp 2-1 loss to 10-man Leeds United.
Pep Guardiola shuffled his pack with this fixture sandwiched between both legs of their Champions League quarter-final with Borussia Dortmund, and his much-changed side fell behind to Stuart Dallas' opener late in the first half.
A red card for Leeds captain Liam Cooper seemingly tilted the game in City's favour and they eventually broke down their undermanned opponents when Ferran Torres equalised 14 minutes from time.
But Marcelo Bielsa's men caught City on the counter as they pressed for the winner, Dallas latching on to Ezgjan Alioski's through-ball and sliding his second through Ederson's legs to clinch a remarkable victory for Leeds.
An unsurprisingly open first half did not result in many clear-cut chances, though Raheem Sterling wasted a gilt-edged one as he fired wastefully wide after an excellent run and pass from Fernandinho.
Leeds did not produce a shot until the 42nd minute, the longest they have waited for their first effort in a Premier League match this season, but the quality of Dallas' strike ensured it was one that gave them the lead.
Following excellent work down the left from Helder Costa, Patrick Bamford laid the ball off for Dallas, whose driven low effort flicked off the inside of the left-hand post and beyond a stricken Ederson.
Yet Leeds' hopes of keeping hold of that advantage were dealt a major blow when, after consulting the VAR monitor, Andre Marriner deemed Cooper had committed a red-card offence in catching Gabriel Jesus high with his studs up.
Illan Meslier produced a fine diving save to keep out Oleksandr Zinchenko's powerful effort from the edge of the area and Bernardo Silva and substitute Ilkay Gundogan, making his 200th appearance for City, each spurned chances to equalise as they predictably dominated the second half.
Meslier was comfortable in saving long-range efforts from Fernandinho and Joao Cancelo but could do nothing to prevent Torres from finally restoring parity.
Fernandinho's incisive pass fed Silva, who slid the ball across to Torres to beat Meslier with a confident finish into the bottom-left corner.
Ederson produced a fine piece of goalkeeping to dispossess Raphinha as he bore down on goal, but Leeds were ultimately rewarded for their unrelenting ambition in the 91st minute as Dallas kept his composure to seal the points.
What does it mean? Bielsa beats Guardiola, and gives Dortmund a blueprint?
Guardiola has never made any secret of his admiration for Bielsa who, having had a significant influence on the City boss' career, now has his first win over the Catalan.
In being forced to play a more defensive brand of football to get it after Cooper's red card, Bielsa might have given Dortmund a formula by which to knock City out of the Champions League.
Teams sitting back against City is nothing new and Kevin De Bruyne, fresh off his contract extension, was kept on the bench. However, City's struggles in breaking down Leeds may give the often defensively fragile Dortmund, who only need a 1-0 win on Wednesday to progress, hope that they can protect a lead should they get ahead at Signal Iduna Park.
The result likely won't affect the destination of the Premier League title, with City still 14 points ahead of Manchester United.
Dallas ends two-decade wait
In securing victory, Dallas became the first player score a 90th-minute winner for Leeds in the Premier League since Ian Harte against Derby County in December 1999. He is the first player to do so for any side against City in a league match since Fernando Torres for Chelsea in October 2013.
Leeds might never have been in a position to claim maximum points had Sterling not been so profligate. He had five shots on goal but only one on target, his early miss after Fernandinho's industrious run his most egregious miscue.
It's a massive week for City's hopes of an unprecedented quadruple, as they face Dortmund on Wednesday and then Chelsea in an FA Cup semi-final on Saturday. Leeds host Liverpool a week on Monday.