Chelsea suffered their first Premier League defeat this season as Edouard Mendy’s embarrassing blunder put Leeds on course for a 3-0 win, while Brighton condemned West Ham to a third successive loss on Sunday.
Mendy’s costly mistake was the catalyst for Chelsea’s shocking implosion at Elland Road as Brenden Aaronson netted after catching the goalkeeper taking too long in possession.
Rodrigo’s fourth goal in three games this season doubled Leeds’ advantage before half-time.
Jack Harrison completed Leeds’ first win over Chelsea since 2002 and their biggest against their old rivals since 1995.
Adding to Chelsea’s misery, their Senegal defender Kalidou Koulibaly was sent off for a second booking after tripping Joe Gelhardt in the 84th minute.
Unbeaten after three games, Leeds sit second in the table as boss Jesse Marsch builds on the momentum established during the club’s successful fight to avoid relegation last season.
In contrast, Chelsea find themselves in the unusual position of sitting below their less glamorous west London neighbours Fulham and Brentford in the table.
Thomas Tuchel’s side have taken four points from their first three games and the German will be concerned at the way his expensively rebuilt team faded after Mendy’s howler.
Marsch had cheekily suggested Tuchel’s one-match touchline ban for his clashes with Tottenham manager Antonio Conte last weekend should have been imposed in time for Chelsea’s trip to Yorkshire.
Tuchel might have wished he could be anywhere but Elland Road as Chelsea collapsed.
Raheem Sterling should have given Chelsea the lead inside the first 60 seconds, but the forward’s penetrating run ended with a shot that curled wide from 12 yards.
Sterling did find the back of the net after 15 minutes, only for an offside flag to correctly rule out what would have been the former Manchester City star’s first goal for Chelsea.
Mason Mount’s low strike forced a save from Illan Meslier as Chelsea looked set to dominate.
But Mendy gifted Leeds the opening goal in the 33rd minute when the Chelsea keeper took too long to clear Thiago Silva’s backpass before attempting a suicidal turn that allowed Aaronson to steal the ball and tap into the empty net.
Not for the first time during his Chelsea career, Mendy had been caught in possession and the embarrassed Senegal keeper held his head in frustration as Aaronson sprinted away to celebrate.
It was the United States winger’s first goal for Leeds since his close-season move from Red Bull Salzburg.
Chelsea were shell-shocked and, just four minutes later, Mendy was beaten again as Rodrigo rose above Reece James to glance a superb header into the far corner from Harrison’s free-kick.
Encapsulating Chelsea’s meltdown, Marc Cucurella wasted a chance to reduce the deficit when the left-back shot tamely wide with the goal at his mercy.
Harrison put the result beyond doubt in the 69th minute when he poked home from close-range after Rodrigo knocked down Daniel James’ cross.
At the London Stadium, Brighton added to West Ham’s woes with an impressive 2-0 victory.
Alexis Mac Allister put Brighton ahead in the 22nd minute after Danny Welbeck was fouled by West Ham’s debutant defender Thilo Kehrer, a £10 million (£11.8million) signing from Paris Saint Germain.
Kehrer claimed the foul had taken place outside the penalty area, but a VAR check decided it was just inside and Mac Allister calmly converted the spot-kick.
Leandro Trossard raced through to bag Brighton’s second goal with a composed finish past Lukasz Fabianski in the 66th minute.
Brighton are in fourth place with seven points from their first three games, while West Ham slumped below Manchester United to the bottom of the table.
Manchester City will take over from Arsenal in first place if the champions beat Newcastle by at least a two-goal margin at St James’ Park in Sunday’s late game.
Pep Guardiola’s side have won the first two matches of their title defence, while unbeaten Newcastle have four points.