The introduction of Pierre-Emerick Aubameyang from the visitors' bench proved to be the turning point in an exciting match that saw Carlo Ancelotti's side surprisingly beaten
There had been few suggestions that PSG had the imagination to break down the visitors in an engrossing first period, yet it still came as a shock when Mamadou Sakho put through his own net to give Sainte the lead.
Ibrahimovic’s red card for a reckless challenge on Stephane Ruffier was fully merited before Pierre-Emerick Aubameyang put the game beyond doubt moments later. Guillaume Hoarau restored some pride with an 88th-minute strike, but by that point the damage had been inflicted.
Carlo Ancelotti’s men had done just enough in midweek to elbow Olympique de Marseille out of the Coupe de la Ligue, but they were impressively contained by Sainte in the first half. Jeremy Menez was the liveliest of the home players, as he fashioned a good chance for Ibrahimovic after 11 minutes only for Ruffier to foil the Swede with a fine block.
That proved to be the only genuine opening of the first 45 minutes. A number of half chances followed, but Menez lifted a shot over from the edge of the box after dancing clear of a couple of challenges while Mamadou Sakho headed over following a corner from the ubiquitous winger.
Things really started to crumble for the capital club when Aubameyang was introduced from the Saint-Etienne bench. Within minutes of arriving on the field, the former AC Milan youth had broken the offside trap and centred with such ferocity that there was little Sakho could do to prevent the ball ricocheting off his leg and into his own net.
Ibrahimovic’s dismissal was the result of desperation as he leaped in an attempt to control a long ball through but succeeded only in clumsily delivering a flying kick to the midriff of Ruffier. After a brief delay to treat the goalkeeper, Ligue 1’s top scorer was brandished with a red card.
Aubameyang’s own exploits this season deserve credit, and the Gabon international came firmly into the spotlight when he added a second for the visitors shortly afterwards to kill the game off with 20 minutes to play. Mathieu Bodmer was carelessly robbed in the midfield, and Sainte ruthlessly exploited the break, with the striker left a simple tap-in.
With two minutes left, Hoarau's fine, late consolation merely served to remind his coach ahead of Ibrahimovic's impending ban.
Carlo Ancelotti’s side remains top of Ligue 1 for the time being, but Toulouse could steal its place if it overcomes Bordeaux on Sunday, while Saint-Etienne has moved to within four points of the summit thanks to a third win in its last four Championnat games.