Bradley Barcola and Goncalo Ramos had PSG 2-0 up in Brittany before Lilian Brassier pulled one back for Rennes, but Dembele netted twice in stoppage time to seal the victory for the visitors.

The result allowed the Ligue 1 leaders to maintain their unbeaten record domestically this season.

The Parisians are now a huge 16 points clear at the top, with closest challengers Marseille losing 1-0 at home to Lens later on Saturday.

Luis Enrique's PSG side were ultimately comfortable winners despite the coach making eight changes to his line-up in between the two legs of the Liverpool tie, with the return at Anfield coming up on Tuesday.

"We are in perfect condition to go and take on Liverpool. We have nothing to lose and we will give everything to try to qualify," for the quarter-finals, said Luis Enrique.

"It was difficult but we put in a serious performance and it gives us lots of hope before going to Liverpool," the Spaniard added of his team's display.

Marseille beaten 

Barcola, Joao Neves and Willian Pacho were the only players to keep their places for PSG against Rennes following the 1-0 home loss to Liverpool in the first leg last Wednesday.

Dembele was among the regular starters to be rested at kick-off, but he came off the bench just after the hour mark and the France forward's double strike moves him onto 20 league goals for the campaign.

The player who began his career at Rennes has now scored 28 times in all competitions this season, including 23 goals in 18 appearances since mid-December.

Rennes came into the game on a run of four wins in five outings to climb into mid-table after Habib Beye replaced Jorge Sampaoli as coach in late January.

However, PSG went ahead at Roazhon Park on 27 minutes as Desire Doue, another former Rennes player, quickly took a free-kick just inside the home half and released Barcola to run through and score his 18th of the season.

Teenage forward Mohamed Kader Meite almost equalised for Rennes before the break, heading off the crossbar from Adrien Truffert's cross.

Barcola then turned provider as PSG doubled their lead five minutes after half-time, squaring for Ramos -- one of those brought into the line-up -- to net his 13th this season in all competitions.

Centre-back Brassier pulled one back for Rennes shortly after, heading in from close range after a corner had been flicked on.

However, Luis Enrique then sent on the cavalry, with Dembele, Nuno Mendes, Vitinha, Khvicha Kvaratskhelia and Achraf Hakimi all coming off the bench for the latter stages.

PSG made sure of the points as Hakimi ran through on goal before unselfishly squaring for Dembele to make it 3-1 in the first minute of stoppage time.

Dembele then fired in his second and PSG's fourth goal from the edge of the area in the 94th minute.

Marseille dominated from the off at home to Lens as they looked to cement their grip on second place.

However, they were denied by an obstinate Lens side and by some inspired goalkeeping from the visitors' Mathew Ryan.

The Australian tipped an Amine Gouiri shot onto the bar in the first half and saved from both Luis Henrique and Neal Maupay late on.

Lens, who had lost their last four matches, then won the game in the 94th minute as Deiver Machado set up Neil El Aynaoui to deliver the sucker punch.

Elsewhere on Saturday, Lille were 1-0 winners at home to Montpellier in a game that fell in between the two legs of their Champions League last-16 tie against Borussia Dortmund.

Jonathan David scored the only goal early in the second half, the Canadian netting his 14th of the campaign in Ligue 1.

Lille are fifth in the table, behind Monaco in fourth on goal difference.

They entertain Dortmund on Wednesday after drawing 1-1 in the first leg in Germany.