Fifth-placed Tottenham were punished for a sloppy performance as the in-form Rodrigo Muniz netted twice either side of Sasa Lukic’s first goal for Fulham.
A 4-0 win at Villa last weekend was expected to act as Tottenham’s springboard to finish above Unai Emery’s team in the battle to qualify for next season’s Champions League.
Instead, the north Londoners crashed to a first league defeat at Craven Cottage since 2008 and failed to score for the first time in 40 games.
They sit two points behind Villa, who can extend that lead to five if they win at West Ham on Sunday.
With Micky van de Ven sidelined by a hamstring injury, Radu Dragusin made his first Tottenham start.
Worryingly for Postecoglou, Romania centre-back Dragusin, signed from Genoa in January, was often exposed in a rocky display.
Fulham took the lead in the 42nd minute when Muniz cleverly drifted away from Dragusin as the Brazilian forward found space to meet Antonee Robinson’s low cross with a clinical finish from 10 yards.
Tottenham’s defensive deficiencies were exposed again four minutes after half-time.
Iwobi was allowed to advance unchecked and he slipped a pass to Timothy Castagne, whose cross hit Lukic and deflected into the net.
Tottenham were in tatters and Muniz struck again in the 61st minute.
Joao Palhinha’s header reached Calvin Bassey and when his shot was saved by Guglielmo Vicario, Muniz reacted quicker than Dragusin to stab home.
‘We’ve got to fight’
As the fight to avoid relegation comes to a head, Luton and Forest met in a vital showdown at Kenilworth Road.
Forest, beaten in their previous three games, took the lead through Chris Wood’s 34th minute strike.
But Luke Berry came off the bench to equalise from close-range in the 89th minute.
Third-bottom Luton, who blew a three-goal lead in Wednesday’s disastrous 4-3 defeat at Bournemouth, are without a win in their last nine games in all competitions.
They lie three points behind fourth-bottom Forest and boss Rob Edwards said: “You get knocked down on Wednesday and it was very tough for us all. We performed really well today in difficult circumstances.
“This group just keep going. We’ve got to fight. We’ve had to do that for a long time.”
Forest boss Nuno Espirito Santo added: “We did enough to win it with the chances we had and the way we played.”
At Turf Moor, second-bottom Burnley kept alive their faint survival hopes with a 2-1 victory against Brentford.
Vincent Kompany’s side took the lead in the 10th minute when Vitinho sprinted onto Josh Cullen’s pass and was about to shoot when he was pulled down by Sergio Reguilon.
The Spanish defender was shown the earliest red card in the Premier League this season, after a VAR check, and Jacob Bruun Larsen stepped up to convert the spot-kick.
David Datro Fofana, on loan from Chelsea, struck in the 62nd minute with a composed finish into the far corner.
Kristoffer Ajer got one back in the 83rd minute with a diving header from Bryan Mbeumo’s cross, but the Clarets held on for their first league win in 11 games.
They are now eight points from safety with nine games left.
“It had been coming. On another day we could have scored more,” Kompany said.
Brentford have won only three of their past 18 league games and sit just four points above the relegation zone.
© Agence France-Presse
Photo: Twitter @FabrizoRomano