The victory lifted them to fourth, two points behind leaders Monaco, who drew on Friday, and Marseille who won earlier Saturday.
"I'd always like things to go the way they did tonight, but in football there are always surprises," said PSG coach Luis Enrique.
"There was a Champions League rhythm," the Spaniard said. "My players were very brave and against a team that defends well. We created a lot of chances."
Mbappe, making his first home start since being reinstated to the team following a contract dispute, posed a threat from the start.
In the first half, he had one shot saved by goalkeeper Brice Samba and another cleared off the line by Kevin Danso before Marco Asensio scored his first goal for the club in the 44th minute.
PSG's Portuguese midfielder Vitinha surged up the field before moving the ball on to Warren Zaire-Emery who passed to Asensio just outside the box. The Spaniard curled a left foot shot in off the base of the post.
Mbappe added a ferocious second after 51 minutes, meeting a return pass from Lucas Hernandez with a first-time side-foot shot from the edge of the box that rocketed past Samba.
Mbappe forced another good save from Samba as PSG dominated possession.
On a rare Lens counter-attack, Elye Wahi, the club's record signing, who came on after 57 minutes, outpaced the home defence and forced a sprawling save from Gianluigi Donnarumma.
Ousmane Dembele, making his first PSG start since moving from Barcelona, lashed an opportunity for a first goal for the club wide.
Mbappe added a second in the 90th minute with a shot from near the penalty spot that took two deflections on its way into the net.
As PSG's defence relaxed, Wahi forced another flying save from Donnarumma before Morgan Guilavogui scored with the last kick of the match, his shot deflecting in off Milan Skriniar.
"In the second half, we opened up and if you open up against this team, things happen too quickly. We didn't give up but there was too much difference between the two teams," said Lens coach Franck Haise.
MARSEILLE END BREST'S RUN
Earlier, Marseille jumped to second place after ending visiting Brest's winning start to season with a lacklustre 2-0 victory.
Knocked out of the Champions League in the third qualifying round by Panathinaikos at the start of the month, Marseille's rebuilt squad had a week to prepare.
The hosts started brightly when Chancel Mbemba opened the scoring with a header from Jordan Veretout's impeccable free kick after three minutes.
Brest, who had opened the season with two wins, dominated the rest of the half and squandered a string of chances.
"In the first half we weren't organised properly, we lost too many balls and Brest were better," said Marseille coach Marcelino, who took over in the summer.
The introduction of Vitinha from the bench lifted Marseille who stretched their lead after 65 minutes.
Ismaila Sarr met a cross from Renan Lodi to score for the first time since arriving from Watford in the summer.
Vitinha created two golden chances for Veretout and Pierre-Emerick Aubameyang, who was wasteful throughout.
"It got better in the second half and after the second goal, we were the Marseille we want to be," said Marcelino. "If we'd been bad throughout, I'd be worried."
