Paris Saint-Germain had Kylian Mbappe to thank as his brace saw the runaway Ligue 1 leaders come from behind to win 2-1 at struggling Caen on Saturday in their final outing before their Champions League last 16, second leg against Manchester United.

A week after reaching a half-century of goals in France's top flight at the age of 20, Mbappe netted a penalty for the first time in his Ligue 1 career just before the hour mark.

That cancelled out Chadian forward Casimir Ninga's opener for Caen, and Mbappe then grabbed the winner in the 87th minute for his 29th goal in all competitions this season.

Of those, 24 have come in the league, including six in the last four games.

This was an eighth successive win for PSG in all competitions, and their enormous lead at the top of Ligue 1 is now 20 points before second-placed Lille play Dijon on Sunday.

"The coach said before the game that to prepare for the big matches we need to win the game before it," Mbappe told Canal+.

"We had a three-hour bus journey to get here and we didn't do that to come and see the tourist sights -- we wanted the victory, and now we are going to go home and focus on what is a very important match."

Coach Thomas Tuchel rested a host of players who are likely to start against United at the Parc des Princes on Wednesday, when Paris will look to follow through on their 2-0 win in the first leg last month.

Gianluigi Buffon, Thiago Silva, Presnel Kimpembe, Juan Bernat, Marco Verratti and Julian Draxler were all either left on the bench or absent altogether.

Neymar and Edinson Cavani are still sidelined, although the latter is now close to a comeback after a hip injury.

"The team worked hard for 90 minutes and to score such a late goal tells you something about our mentality," Tuchel told Canal+.

"Now we must analyse Manchester United again. They have some players missing and now they are doing things a bit differently so we need to look at what team we will put out."

United's 3-2 win over Southampton on Saturday continued their fine run under Ole Gunnar Solskjaer, with the first leg against PSG remaining the Norwegian's only defeat in charge.

PSG's humiliating collapse against Barcelona two years ago after they won the first leg 4-0 ensures they are not getting carried away.

"It's not good to play with fear, but it's not good to play with too much confidence either," added Tuchel.

"We have guys who played in Barcelona, who have that experience.

"We can't control the result, you never can in football, but we can control our performance."

PSG had hit the woodwork three times in the first half in Caen, through Layvin Kurzawa, Marquinhos and Angel Di Maria.

The latter had a goal disallowed for offside too, but Caen also hit the frame of the goal in the first half via Enzo Crivelli's header.

The Normandy side looked as if they might get their first league win of 2019 when they went ahead in the 56th minute, Faycal Fajr sending a free-kick through to Ninga, who controlled on his thigh and fired home.

However, PSG were level within three minutes when Mbappe scored from the spot after a handball by young defender Younn Zahary.

Di Maria then sent a header against the post soon after, but Paris won it with three minutes left, Mbappe scoring from two yards after a Thomas Meunier shot had been blocked.

Caen remain in the relegation play-off place and are now five points behind 17th-placed Amiens, who drew 2-2 at Reims.

Monaco are another point better off in 16th after coming from two goals down to draw 2-2 at Angers, Radamel Falcao scoring twice.