Mollo grabbed his third goal of the season after beating goalkeeper Benjamin Lecomte with a slightly deflected shot in the 75th minute, and Gradel turned in Romain Hamouma’s cross to seal the win in the 90th.
Saint-Etienne are one point behind Monaco, having played a game more.
Guingamp 0, Lille 1
Lille made it back-to-back Ligue 1 wins for only the second time this season as Nolan Roux clinched a 1-0 triumph at Guingamp.
Roux looped home over Guingamp goalkeeper Jonas Lossl six minutes after the interval and Lille held firm to maintain momentum after their 2-1 victory over Lyon last week.
The win moves Les Douges up to eighth in the table, while Guingamp remain 12th – just six points above the drop zone and in desperate need of rediscovering their goalscoring touch.
Going into this clash the hosts had gone more than three hours without finding the back of the net in the league, but early signs indicated that barren run was not going to end against a determined Lille side in a bruising encounter.
Both Simon Kjaer and Franck Beria needed lengthy treatment early on for the visitors, the latter being forced off permanently, before Vincent Enyeama became the first keeper to be tested on 20 minutes, superbly keeping out Thibaut Giresse’s close-range control-and-volley.
Lille responded but Liverpool loanee Divock Origi saw his shot well blocked by Christophe Kerbrat before Florent Balmont had a speculative effort from distance drift wide.
With the scores level at the break, the visitors came back out with real intent and Djibril Sidibe went close with a 20-yard drive that threatened the crossbar before Rene Girard’s side edged their way in front.
Roux began the move and finished it when his pass found Lopes whose return ball into the area was looped over Lossl by the 27-year-old striker.
Lossl was almost beaten again soon after when Balmont’s free-kick almost drifted beyond him but the former Denmark Under-21 stopper tipped the ball to safety.
A late flurry from the hosts did come but Lille keeper Enyeama stood up to the test well, making a magnificent reflex save to keep out Christophe Mandanne’s point-blank effort in the final 10 minutes to ensure a maximum points haul for Les Dogues.
PSG beat Lens 4-1 on Saturday with striker Zlatan Ibrahimovic getting his 12th league goal of the season.