In the fourth minute of added on time the Swedish international headed a corner into his own net to deny Daniel Farke’s team of a deserved point and extend their dire Premier League record in the capital to nine successive defeats.
United were within touching distance of a precious point when a corner from the right evaded everyone but Gudmundsson who was unable to react quick enough to deal with the danger as the ball cannoned off his forehead past the helpless goalkeeper Karl Darlow.
It was a cruel way to lose a game but Farke refused to blame Gudmundsson for the defeat.
The Leeds boss described the goal as “one in 10,000.”
“It’s difficult to explain. He was concentrated on blocking the player, lost control of his body and was surprised by the ball. He was excellent today, there with an excellent performance. He was so crucial for our game, a top performance. That he’s there with the spotlight is unlucky for him.”
After four games in their return to the top flight Leeds have yet to score a goal in open play – their only strike coming from the penalty spot in the season’s opening win against Everton.
In an effort to pep up his attack Farke changed his entire frontline handing first Premier League starts to Dominic Calvert-Lewin and Noah Okafor alongside Brenden Aaronson on the right.
Apart from occasional flashes from Okafor, Leeds still looked lightweight in attack in a game of few chances. Calvert-Lewin nodded a free header into the arms of goalkeeper Bernd Leno after 15 minutes and Sean Longstaff grazed the bar with a fierce effort just before the interval.
Aaronson forced a good block from Leno just after the break and at that stage sluggish Fulham hadn’t registered an effort on target as they could find no way round or through a well-organised Leeds unit.
Twin midfield anchors Ethan Ampadu and Sean Longstaff did a brilliant job breaking up Fulham’s attacks to protect a solid defensive unit behind them. Leeds looked comfortable.
Darlow’s first meaningful save didn’t come until just before the hour when he tipped away a free-kick fizzer from Harry Wilson who almost joined Leeds on deadline day.
Soon afterwards the introduction of Emil Smith-Rowe and Adama Traore gave Fulham a bit more impetus with striker Rodrigo Muniz, a summer target for Leeds, directing a tame header at Darlow but the real game changer was Brazilian winger Kevin, Fulham’s club-record £34.6m signing from Ukrainian club Shakhtar.
The Cottagers chief Marco Silva sent him on for his debut with 15 minutes of the 90 remaining and the 22-year-old made an instant impact with some dazzling, speedy footwork. He quickly set up a chance for Sasa Lukic, which the Serb could not take, then drew a brilliant flying save from Darlow, in for the injured Lucas Perri, at the expense of the match-winning corner.