Ousmane Dembele scored on his return from injury as defending champions Paris Saint-Germain thrashed Bayer Leverkusen 7-2 in the Champions League on Tuesday, as both teams finished with 10 men.

Ballon d'Or winner Dembele scored PSG's sixth just three minutes after coming on as a second-half substitute for his first appearance since suffering a hamstring injury in early September.

Desire Doue bagged a brace while Willian Pacho, Khvicha Kvaratskhelia, Nuno Mendes and Vitinha also hit the net at Leverkusen's BayArena as the visitors laid down the gauntlet to their European rivals.

"We are a team that always wants to win everything. This season, we want to win everything again," PSG coach Luis Enrique said.

"That will be difficult but we have the confidence we gained last year. We want this title again."

Aleix Garcia scored both of the hosts' goals while PSG lost centre-back Illia Zabarnyi to a red card on 37 minutes, as he conceded a second spot-kick of the match.

Leverkusen also had captain Robert Andrich dismissed for crashing his elbow into Doue's jaw a few minutes earlier.

Leverkusen coach Kasper Hjulmand told Amazon Prime that his side "lost it in seven minutes before halftime".

"We were level but we wanted too much," he added. "We were too open and made too many mistakes in that seven-minute period.

"We met the best team in the world right now. They're very strong."

PSG have been injury-hit and inconsistent this season, but once both teams were reduced to 10 men, they dominated their hapless hosts.

PSG's bid to go back-to-back on the European stage will face tougher tests than the rebuilding Leverkusen, who fielded six starters who only joined the club in the summer.

The French champions showcased their attacking riches alongside the steel needed to overcome setbacks borne out of last year's breakthrough campaign.

- Dembele starts on the bench -

PSG's preparation for the game was boosted by the news that Dembele and captain Marquinhos were fit enough to make the trip to Germany.

The duo, crucial to PSG's barnstorming treble last season, watched on from the bench as PSG took the lead after just seven minutes.

Mendes hit a cross over the Leverkusen defence for Pacho to head in at the far post.

Leverkusen were awarded a penalty for a Zabarnyi handball with 25 minutes gone but Alejandro Grimaldo hit the post with his spot-kick.

The writing looked to be on the wall for Leverkusen when they were reduced to 10 men by Andrich's needless foul on Doue on 33 minutes.

But they were then handed a lifeline shortly afterwards when Zabarnyi's performance went from bad to nightmarish as he gave away a second penalty and saw red for clumsily bringing down Christian Kofane as the last man, with Garcia scoring from the spot.

Rather than tighten up, the red card galvanised the French side, who reacted by scoring three goals in eight minutes to stun the hosts.

Doue scored twice either side of a Kvaratskhelia scorcher to go into the break 4-1 up and cruising.

Mendes scored five minutes into the second half to help PSG pick up where they had left off.

While Garcia's long-distance stunner on 54 minutes was a rare Leverkusen highlight, PSG had the last words.

Dembele cut the ball home from a tight angle and Vitinha added even more gloss on the final score, rounding out an incredible European night for the defending champions.