Lionel Messi scores his side's 3rd goal, challenged by Lens' Jonathan Gradit during the match in Paris on Saturday night. AP

Lens, who began the day six points behind league leaders PSG in second place, looked the better team until Ghana midfielder Salis Abdul Samed was dismissed for a dangerous challenge on Achraf Hakimi in the 19th minute.

That changed everything, and by half-time the hosts were out of sight thanks to three goals in the space of 10 minutes from Kylian Mbappe, Vitinha and then Messi, with Przemyslaw Frankowski pulling one back for Lens from a penalty.

Mbappe opened the scoring and Vitinha's long-ranger doubled PSG's lead in the 37th minute.

Both goals were good but Messi's that made it 3-0 was stunning, the Argentine finding a pocket out of space outside the area, feeding a pass to Mbappe and then receiving the France striker's backheel return before slotting beyond goalkeeper Brice Samba and into the far corner.

The result leaves the reigning champions nine points ahead with seven games left, meaning it is surely just a matter of time until PSG secure a French record 11th league title.

"We must not think that it's done and dusted," said coach Christophe Galtier. "We will need to remain serious and determined to maintain our lead and not give any hope to the teams chasing us."

The win comes at the end of a week overshadowed by allegations of racism against Galtier, who had already been under pressure since PSG's elimination from the Champions League last month.

Galtier said on Friday that he was "deeply shocked" by accusations that he made racist and Islamophobic remarks about Nice players when he was in charge there last season.

The allegations surfaced in an email apparently sent by former Nice sporting director Julien Fournier and which have been reported by various French media. AFP has not been able to verify the message.

The affair looks set to hang over the coach and the club in the coming weeks.

"I was very determined and focused on the match, like my players," Galtier said of trying to stay concentrated on the game. "It was obviously an important match, if not decisive, and so it was important to get the result and enjoy it."