Jamie Vardy was the scourge of Manchester City again as his hat-trick secured a sensational 5-2 win for Leicester City and raised fresh questions about Pep Guardiola's defence.
The striker won two penalties and converted both, either side of a terrific backheeled finish for his second goal, to net his second hat-trick against City – almost four years after his treble in a 4-2 victory over the same opponents.
His former Leicester teammate Riyad Mahrez gave the hosts the lead at the Etihad Stadium on Monday (AEST), but Vardy then took centre stage, with James Maddison adding a brilliant fourth goal late on.
Nathan Ake headed a City consolation, but Leicester then scored a fifth in a dramatic Premier League clash, with Maddison fouled and Youri Tielemans slotting in another penalty.
It meant Guardiola, in his 686th game as a manager, suffered the indignity of seeing one of his teams conceding five goals for the first time.
City lacked a senior striker, with Sergio Aguero and Gabriel Jesus injured, and it showed. Winger Raheem Sterling was deployed in a central role, but he was kept quiet and Guardiola called on 17-year-old Liam Delap early in the second half, sacrificing Fernandinho.
How Guardiola must have wished he had a striker of Vardy's quality to summon. He might welcome a less brittle defence, too, after problems at that end of the field were a key reason they failed to seriously challenge Liverpool last season.
Mahrez hit a stunning opening goal after three minutes, finding the top-left corner with a rasping right-footed strike after Kevin De Bruyne's corner from the left was only half cleared.
Rodri then had a goal disallowed after straying offside before heading in a free-kick from De Bruyne. But moments later, in the 37th minute, Leicester drew level.
Vardy went down under a lazy challenge from Kyle Walker, and the former England frontman smashed the spot-kick high into the net.
The clinical striker made the home team suffer for a second time in the 54th minute when he produced a tasty flick to convert Timothy Castagne's low cross from the right.
Leicester had a second penalty moments later when Vardy went down under a challenge from Eric Garcia, and Vardy this time found the bottom-right corner.
Substitute Maddison added a fourth in the 77th minute, cutting in from the left and curling a sumptuous shot over Ederson, before Ake headed in at the other end.
There was still time for a third Leicester spot-kick, and with Vardy off the field by that point due to what appeared to be a groin issue, it was Tielemans who stepped up to put the finishing touch to an annihilation of Guardiola's backline.
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Ruben Dias had better be good. Guardiola is poised to lure the Benfica defender to Manchester and must hope he can be the man to bring some authority to his rearguard.
The men in blue were a calamity at the back, just as they were at times last season.
Jamie's magic touch
Vardy was immaculate from the penalty spot, but the pick of the goals from last season's Golden Boot winner was his ingenious finish for Leicester's second.
Castagne darted in from the right and fed a low ball to the near post, with Vardy producing what he said teammates were already calling "a Johan dink". Is there a touch of Cruyff about Vardy? Doubtless the late Dutch legend would have admired that finish.
Vardy had just eight touches in the first half and 21 in all, but didn't he make them count as Leicester made it three wins out of three in the top flight, rising to the summit.
Pep's big problem
Garcia and Benjamin Mendy – who brought down Maddison – each gave away spot-kicks with rash challenges. Leicester became the first team in Premier League history to score three penalties in one game, with City shipping five at home for the first time since a 5-1 walloping by Arsenal at Maine Road in February 2003.
Manchester City make the short trip to Burnley on Thursday (AEST) in the EFL Cup fourth round, before tackling Leeds United in the Premier League on Sunday. Leicester are out of the EFL Cup and host West Ham next Sunday in the Premier League next time out.