As expected, Federico Valverde lined up at right-back for Real Madrid due to the team's injury problems, while there was a full debut in the middle of their defence with Raul Asencio.
Dani Ceballos and Arda Guler also started, with head coach Carlo Ancelotti shuffling his pack, and it was hard work for the reigning champions for long stages of the opening half of action.
Real Madrid had to wait until the 43rd minute of the match to make the breakthrough, with Kylian Mbappe turning a low cross from Vinicius Junior into the back of the net to silence the home team's supporters.
Los Blancos then doubled their lead in the 66th minute, with Valverde's strike from outside the penalty box flying into the bottom corner, as a clever short free kick allowed Ancelotti's side to make it 2-0.
Jude Bellingham also got his name on the scoresheet in the latter stages, with the midfielder heading into the back of the net from close range after a strike from Brahim Diaz had been deflected onto the crossbar.
In truth, Leganes never threatened to make it a contest, and the defeat has left the promoted outfit in 14th spot in the table, four points ahead of the relegation zone, so it has been a successful campaign for Borja Jimenez's side to date.
LEGANES VS. REAL MADRID HIGHLIGHTS
Kylian Mbappe goal vs. Leganes (43rd min, Leganes 0-1 Real Madrid)
Real Madrid make the breakthrough in the 43rd minute of the contest, with Mbappe turning into the back of the net from close range after a low cross from Vinicius; Los Blancos have lift-off here, with Leganes undone just before the break.
Federico Valverde goal vs. Leganes (66th min, Leganes 0-2 Real Madrid)
Real Madrid double their lead in the 66th minute of the contest through Valverde, with the midfielder's low shot from outside the box finding the corner; a free kick was played short to the Uruguay international, and he hammered one into the back of the net.
Jude Bellingham goal vs. Leganes (85th min, Leganes 0-3 Real Madrid)
Real Madrid make sure of the points in the 85th minute, with Bellingham getting his name on the scoresheet; the Englishman heads into the back of the net from close range after a Brahim strike had been deflected onto the crossbar.
MAN OF THE MATCH - FEDERICO VALVERDE
Valverde has been outstanding for Real Madrid this season, and that was again the case on Sunday, with the Uruguayan starring in a right-back role, having been required in that area due to the team's injury problems.
The midfielder scored Real Madrid's second with a brilliant effort in the second half, but his overall performance is what earns him the man-of-the-match award, with Valverde also completing 56 of his 59 passes at Estadio Municipal de Butarque.
LEGANES VS. REAL MADRID MATCH STATS
Possession: Leganes 32%-68% Real Madrid
Shots: Leganes 4-16 Real Madrid
Shots on target: Leganes 0-9 Real Madrid
Corners: Leganes 2-4 Real Madrid
Fouls: Leganes 17-11 Real Madrid
BEST STATS
WHAT NEXT?
Real Madrid's attention will now switch to the Champions League, with Los Blancos heading to Liverpool on Wednesday night, before returning to La Liga action at home to Getafe next Sunday.
Leganes, meanwhile, will be bidding to bounce back from their sixth league defeat of the campaign when they head to Alaves on Saturday.