Late substitute Lucas Ocampos made an almost-immediate impact with an 87th-minute winner as Monaco opened up a three-point cushion at the Ligue 1 summit on Saturday evening with a 2-1 victory over St Etienne.

Romain Hamouma looked to have earned Les Verts a point when he equalised four minutes into the second half, cancelling out Belgian midfielder Yannick Ferreira Carrasco's 15th-minute opener at the Stade Louis II.

But Ocampos, on as an 84th-minute replacement for Ferreira Carrasco, had other ideas and wasted no time in turning the game in the hosts' favour.

The win moved Claudio Ranieri's side three points clear of champions Paris St Germain and four ahead of third-placed Marseille ahead of their blockbuster clash at the Stade Velodrome on Sunday night.

Monaco could have gone ahead as early as the ninth minute, when Joao Moutinho seized on a poor back-pass from Renaud Cohade and forced a fine close-range save from Stephane Ruffier, but the home fans did not have to wait too much longer to see the game's first goal.

Six minutes later, Ferreira Carrasco controlled James Rodriguez's cross and drilled a left-footed shot past Ruffier.

Ruffier had to be at full stretch to keep the visitors only one down in the 27th minute, diving to his right to keep out Rodriguez's fierce effort from Moutinho's pass.

St Etienne mustered their first opportunity of note on the half-hour mark, but Monaco goalkeeper Danijel Subasic was able to deflect Franck Tabanou's shot away for a corner.

Christophe Galtier's team continued on the front foot after the interval, though. Subasic had to be alert to save Kurt Zouma's header from a Yohan Mollo cross in the 48th minute, but moments later they were level.

Faouzi Ghoulam started the move on the left by freeing Cohade, whose neat flick set up Hamouma to despatch a low left-footed drive past Subasic.

It was backs-to-the-wall stuff for the visitors thereafter as Monaco searched for a winner.

Ruffier and the St Etienne back line stood firm for over half an hour, though, and looked set to depart with a point - Ruffier pulled off a couple of crucial saves including a brilliant reflex stop from a Rodriguez blast which had looked goal-bound just before the hour mark.

However, Ranieri's later tinkering proved decisive. Ocampos - dropped from the starting line-up - was introduced in place of Ferreira Carrasco and needed only three minutes on the pitch before volleying home Rodriguez's excellent cross to the far post.