PSG remain top at Ajaccio's expense
Argentina winger Ezequiel Lavezzi and France midfielder Blaise Matuidi scored, with star striker Zlatan Ibrahimovic setting up both despite having a poor game by his high standards.
Forward Eduardo gave Ajaccio the lead in the sixth minute after being set up by right winger Benjamin Andre, and the Corsican side looked comfortable in the first half, with the lively Johan Cavalli causing problems with his probing runs from midfield.
''We were playing against a team fighting for survival. They created chances but so did we, so I think it's a fair result,'' Matuidi said. ''The pitch wasn't easy to play on either, it was very dry. It did bother us a bit. But let's not look for excuses - the main thing is that we won and that we keep moving forward.
''It's good to win and keep that gap. We've shown that we'll be there (at the end) and we won't give up.''
Lille can overtake Monaco and move into second place if it beats Reims at home on Sunday.
After striker Edinson Cavani missed two chances, PSG cut through Ajaccio's defense easily for the equalizing goal in the 41st.
Cavani collected the ball in midfield from Ibrahimovic, turned and passed to Matuidi, whose pass released Ibrahimovic behind the defense and his cross from the right gave Lavezzi a comfortable finish from close range.
Ibrahimovic made a sloppy start to the second half, and it was a rare sight to see him casually giving possession away several times, even failing with one easy cross from the left as he let the ball slip away from him.
Ajaccio almost regained the lead in the 68th when Cavalli's fine pass released Eduardo, and his shot from the right side of the penalty area forced goalkeeper Salvatore Sirigu into a low save.
Shortly after, coach Laurent Blanc made two changes as he tried to spark some life into his listless team - taking off center half Alex and bringing on playmaker Javier Pastore, and replacing Lavezzi with winger Lucas Moura. Blanc switched to a 4-4-2 formation and Cavani moved in from the right to join Ibrahimovic in attack.
Moments later, PSG scored after a brilliant piece of skill from Pastore. The Argentine dragged the ball back and turned to hit a swerving pass over the Bastia defense. Ibrahimovic rose at the back post to head the ball down and Matuidi sprinted in to turn the ball past goalie Guillermo Ochoa.
''Even though they had a lot of possession, I think we were hanging in there and looked solid, but that goal hurt us,'' center half Ricardo Faty said.
Eduardo went close in the 83rd when he slid in at the back post, but his shot hit the side-netting, and midfielder Paul Lasne headed wide when well placed after running onto Eduardo's cross from the left.
Ochoa made a great reflex save with his left foot to deny Cavani in the last minute.