Leeds extended their winless run to seven games as Nottingham Forest prevailed 1-0 at the City Ground.
Brennan Johnson's 14th minute volley won it for the hosts, whose victory leaves Leeds above the relegation zone only on goal difference.
Pascal Struijk could only glance clear Morgan Gibbs-White's free-kick delivery to Brennan Johnson, who unleashed a fierce low volley into the bottom corner from outside the penalty area.
READ MORE: Beren Cross' Leeds United player ratings from Forest defeat
Wilfried Gnonto was a constant menace down the left and he generated Leeds' best opportunity of the first half. The Italian international surged inside to tee up Patrick Bamford, only for the Leeds forward to fluff his lines.
The loose ball presented itself to Luke Ayling but his tame shot was palmed away by Forest debutant Keylor Navas between the sticks.
Leeds were dominant in the final third in the first half but failed to convert a number of chances. Luis Sinisterra was unable to connect convincingly with Gnonto's low delivery to the near post, before Gnonto forced another save from Navas just before the break.
Marsch presented Weston McKennie and Georginio Rutter with their Premier League debuts from the bench, but it was Steve Cooper's changes that made the biggest impact.
Cooper introduced Serge Aurier and Jack Colback at the break to stifle the threat of Gnonto in the second half. The teenager was starved of the freedom that he was granted in the first half, and Leeds ultimately lost a major attacking outlet as a result.
Leeds have picked up just two wins in their last 17 Premier League games.
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