Leeds United's eight-game unbeaten run came to a juddering halt on Saturday after former manager Garry Monk guided Birmingham City to a 2-1 upset at Elland Road.
Che Adams struck twice to lift the visitors to their first win of the season and condemn Marcelo Bielsa to a maiden Championship defeat.
There was some good news for the Whites, however, with second-placed Middlesbrough failing to take full advantage, held 0-0 at home by Swansea City.
Elsewhere, a John McGinn stunner was not enough for Aston Villa to avoid a 2-1 defeat, while West Brom closed to within a point of the top two.
ADAMS AT THE DOUBLE FOR BIRMINGHAM
Birmingham cast aside an unconvincing run of four successive draws to deal Leeds their first real setback of the season.
Adams stunned the home support with a curious opener in the eighth-minute, wrong-footing Bailey Peacock-Farrell with a quickly taken attempt that crept inside the near corner.
The ex-Sheffield United striker popped up again before the half-hour to put the match beyond Monk's former employers, whose persistent pressure resulted in nothing more than an 85th-minute consolation from Ezgjan Alioski.
Leeds still remain top on goal difference after Middlesbrough failed to find a way past Swansea in a scoreless draw at Riverside Stadium.
FT - Leeds 1-2 Blues— Birmingham City FC (@BCFC) September 22, 2018
Che Adams first-half brace earns Blues their first win of the season! Alioski reduced the scoreline on 85 minutes and Blues then had to see out a bizarre eight minutes of added time.
A hard-earned and well deserved victory! GET INNNNNNN!
MORE BAD NEWS FOR BRUCE
Scotland midfielder McGinn scored a contender for the goal of the season at Villa Park in what was ultimately a losing cause against Sheffield Wednesday.
Marco Matias put Wednesday ahead shortly after half-time, before McGinn responded four minutes later with a sublime sliced volley that left Cameron Dawson with little chance.
Villa's goal tweet containing a questionable rendering of the goalscorer's face in FIFA 19 raised a smile but, in the 67th minute, the mood nosedived.
Steven Fletcher headed home a Joey Pelupessy cross to ensure the Owls leapfrogged their hosts into 10th, increasing the pressure on Steve Bruce.
WEST BROM CARRY ON WINNING WAYS
West Brom are looking increasingly like promotion material, moving to within touch of the top two thanks to a late 2-0 success against struggling Millwall.
Dwight Gayle and Kieran Gibbs both struck in an eight-minute spell beyond the hour that boosted the Baggies' unbeaten run to four matches, while leaving Neil Harris' side languishing in the bottom three.
Elsewhere, Derby County recovered from an early deficit to beat Brentford 3-1, keeping them level on 16 points with a Sheffield United side that edged Preston North End 3-2 thanks to David McGoldrick's 87th-minute winner.
Stoke City were on the opposite side of the same scoreline against Blackburn Rovers, Saido Berahino's missed penalty in stoppage time costing the home side what would have been a rousing three-goal fightback.
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