Despite racing ahead through Javier Pastore's strike and a Zlatan Ibrahimovic penalty, PSG had to settle for a point as St Etienne's spirited response delivered an Alex own goal and a Francois Clerc equaliser.
St Etienne remain unbeaten in 2013 but will be disappointed not to have claimed the three points that would have taken them level on points with Marseille in third.
David Beckham made his first start in European football in almost three years for the visitors and it was PSG who made the perfect start inside 10 minutes.
Ibrahimovic touched the ball into the path of Pastore and he neatly lifted the ball over Stephane Ruffier after Moustapha Bayal Sall hesitated in possession.
Things got even better for the visitors in the 18th minute when Ruffier brought down Ezequiel Lavezzi in the area and the referee awarded a debatable penalty.
Ibrahimovic took charge and, despite having to take the spot-kick twice, he calmly sent Ruffier the wrong way with a clever chip.
Brandao managed to evade Alex in the PSG penalty area as Les Verts pressed in search of a reply but the Brazilian's effort from a tight angle was blocked.
A St Etienne goal did arrive in the 38th minute when Alex touched the ball into his own net. Pierre-Emerick Aubameyang got to the right byline and swung a dangerous cross which the PSG defender could only push beyond Salvatore Sirigu while under pressure from Brandao.
The hosts almost levelled just before the break when Clerc's dangerous cross-shot forced Sirigu into an uncomfortable save down low.
Neither side showed signs of sitting back after the restart and Maxwell got forward early on for PSG but his powerful volley was just an inch over the crossbar.
At the other end Aubameyang was proving a useful outlet for the hosts with his direct running and Brandao could have done better when heading over from close range.
St Etienne continued to look for the equaliser and Aubameyang showed good pace to beat Gregory Van der Wiel on the left before testing Sirigu with a stinging effort.
The hosts' hard work paid off in some style though with just over a quarter of an hour left to play.
The PSG defence failed to clear their lines and the ball fell at the feet of Clerc who guided the ball into the top-left corner with the outside of his right boot.
Beckham was given an opportunity to score with a trademark free-kick moments from the end but the former England captain dragged his effort wide of the right post.