Returning substitute Mauro Icardi gave Paris Saint-Germain a remarkable 3-2 win at home to Saint-Etienne on Sunday to significantly boost the champions' title hopes.

A perplexing encounter was goalless until the 77th minute when Denis Bouanga had Saint-Etienne in front and PSG, beaten in their previous three home Ligue 1 games, facing defeat again.

Kylian Mbappe levelled just 84 seconds later, though, and then won and converted a penalty to seemingly win the match and close to within a point of leaders Lille, held by Montpellier on Friday.

Yet that was far from the end of the drama, with an awful error from stand-in PSG goalkeeper Sergio Rico gifting Romain Hamouma a 92nd-minute equaliser.

Saint-Etienne had just three more minutes to see out to protect a point but allowed Icardi, back after a month out with a thigh strain, to reach Angel Di Maria's cross and nod in to spark jubilant celebrations.

Mauricio Pochettino's side had gone closest before the ludicrous finish, with Pablo Sarabia's 25-yard free-kick bouncing back out off the post before Danilo Pereira hacked the rebound over.

Mbappe played in Rafinha for a low shot that was well saved and then seized on Miguel Trauco's slip and raced into the box before slashing a wild finish over.

But a stale second half threatened to play out without major event until Bouange steered in Trauco's cross.

Rather than clinch the points, that goal simply prompted an outrageous stretch in which PSG went straight up the other end to restore parity as Mbappe smartly controlled a searching Ander Herrera pass and beat Etienne Green.

Mbappe was soon felled by Green and dispatched the subsequent spot-kick, yet PSG improbably threatened to throw away the win as Rico dropped the ball at Hamouma's feet.

Back came PSG and Di Maria, who shortly before had hit the post direct from a corner, helped finally find the match-winner by crossing from the right for fellow sub Icardi to get up highest and head home at the far post.

What does it mean? PSG missing stars but not spirit

Especially with Icardi, Di Maria and Marco Verratti all starting from the bench, this was an undermanned PSG line-up. The suspended Neymar, in a white fur coat, watched from the stands alongside injured goalkeeper Keylor Navas. Marquinhos was also out.

With Neymar on the pitch, PSG might have had more than one shot on target in the first half. They certainly would not have conceded to Hamouma with Navas involved; their outstanding first-choice keeper has not made a single error leading to a goal all season while making 111 saves.

But PSG's spirit could not be questioned. They fought and fought and, with six seconds of the indicated additional time remaining, were eventually rewarded.

Reinforcements to the rescue

Given the talent in the stands and on the pitch, the PSG bench spoke of the strength in depth at Pochettino's disposal. Neither Icardi nor Verratti featured as the French giants beat European champions Bayern Munich over two legs.

They could yet have a say in the Champions League semi-finals against Manchester City, however. While Verratti created two chances and played 17 passes in the Saint-Etienne half, Icardi made the most of his only opening.

Mbappe made to work again

Due to the number of absentees, Pochettino cannot afford to rest Mbappe, who endured some rough treatment. The forward won only a single foul, for the penalty, but hobbled out of an early challenge and required treatment after a late lunge from Harold Moukoudi in the penalty area.

With European opponents City losing Kevin De Bruyne to injury earlier this weekend, PSG might be wary of pushing their own star performer too far. He had to play the full match, had a game-high six shots and a joint-high two key passes.

Key Opta Facts

- PSG have not lost any of their past 16 Ligue 1 games against Saint-Etienne (W11 D5); only against Angers (21) and Brest (18) are they on a longer unbeaten run against current French top-flight sides. 
- The capital club have scored in each of their past 20 Ligue 1 games against Saint-Etienne (49 goals in total), their joint-longest such run against a specific opponent in the top flight (level with Nantes).
- Only Reims (22) and Nantes (20) have lost more points than Saint-Etienne (19) from winning positions in Ligue 1 this season.
- The five goals scored between the 77th minute and full-time were the most in a Ligue 1 game since the same number in Lens' 4-4 draw with Reims last November.
- Mbappe has scored 87 goals for PSG in Ligue 1, surpassing Mustapha Dahleb (85) for the outright third-most in their history. He is now only behind Zlatan Ibrahimovic (113) and Edinson Cavani (138).

What's next?

There is no rest for treble-chasing PSG. They have Angers in the Coupe de France quarter-finals on Wednesday. Saint-Etienne do not play again until Saturday's league clash with Brest.