Monaco had slipped up in the race for the second automatic Champions League spot last weekend when they drew 1-1 at Stade Rennes but responded well to beat Guingamp.
They won with goals from Lacina Traore, Nabil Dirar and Bernardo Silva despite letting the visitors back into the match late on.
The win takes Monaco to 62 points with two games left but Lyon, on 59, would overtake them with a win over Ajaccio before the rivals meet at the Parc Olympique Lyonnais next weekend.
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"We're on the right track, and we can prepare more serenelyfor our 'final' against Lyon with this result," Monaco midfielder Tiemoue Bakayoko told beIN Sports.
"If we're going to achieve our objective we need to stayprofessional, aggressive and cut out these little errors."
Monaco, desperate to finish second after missing out on the Champions League group stage following a playoff defeat by Valencia this season, took control through Traore's deft effort in the 17th minute and Dirar's deflected strike in the 40th.
Mevlut Erding halved the deficit with a close-range finish in the 75th after Ricardo Carvalho and Wallace failed to clear their lines, but Monaco responded instantly with Bernardo Silva beating Lossl with a low shot.
Thirteenth-placed Guingamp set up a nervy finale when Benjamin Angoua headed home in the 81st minute, but were unable to rescue an unlikely point.
Nice slipped to fifth still on 58 points after missing the chance to put pressure on the top three with a 1-0 defeat at Nantes where Adrien Thomasson scored the only goal.
St Etienne, whose captain Loic Perrin was sent off for a late tackle, moved into fourth on 58 points after being held 0-0 at home by Toulouse. The visitors had a fifth-minute penalty from Wissam Ben Yedder saved by Stephane Ruffier.
Corrects transposed names in last line.
(Editing by Ken Ferris)
