The France midfielder, who is suspended for the second leg of Madrid's Champions League quarter-final away to Manchester City next week, scored three minutes into the second half with a deflected 25-metre drive. Jude Bellingham rattled the crossbar in the first half with a rasping effort from just outside the area as Ancelotti reshuffled his attack with Wednesday's trip to England in mind, leaving out Vinicius Junior and Rodrygo.
Tchouameni's third goal of the season put Madrid ahead, with Brahim Diaz denied a second by the legs of Mallorca goalkeeper Predrag Rajkovic and Fede Valverde's attempt cleared off the line. Sergi Darder's spectacular dipping shot forced a flying stop from Andriy Lunin as Madrid extended their unbeaten league run to 25 games, keeping Barcelona a safe distance behind ahead of next week's Clasico in the Spanish capital.