PSG, who held Barcelona to a 1-1 draw on Wednesday but went out of the Champions League on away goals, were far below their usual high standard of play.
"It was very difficult because we did not have much time to recover. We know it's not an excuse but we don't have the experience of dealing with these situations," PSG goalkeeper Salvatore Sirigu told French television Canal Plus.
"We just want to do our job and we have to improve. We can't afford repeating what we did in the first half tonight."
Matuidi made the difference by converting a rare chance when he shot past goalkeeper Yohann Thuram-Ulien from a Gregory Van der Wiel cross.
PSG have 67 points and are 10 above Marseille with six games remaining.
"Ten points is a big gap but Marseille and Lyon are still to play. We'll have to be careful until the end," added Sirigu.
Marseille visit Lille, fifth with 52 points, on Sunday.
The league leaders created their first chance after three minutes when Kevin Gameiro, replacing the suspended Zlatan Ibrahimovic up front, was put clear through on goal by Marco Verratti only to see Thuram-Ulien deny him.
Troyes made some fine moves and went close after eight minutes but Stephane Darbion's powerful effort struck the post.
The hosts continued to push for the opener but never managed to beat a solid Sirigu, who parried away Marcos and Fabien Camus efforts midway through the first half.
PSG regrouped after the break but Thuram-Ulien saved Ezequiel Lavezzi's 47th-minute attempt from a close angle before watching a Matuidi volley go just wide.
The latter moved to an attacking midfielder position when Gameiro was subbed off just after the hour mark and made the most of it within three minutes by scoring his fourth league goal of the season to leave Troyes seven points from safety.
"The only position where Matuidi can't do well is goalkeeper," coach Carlo Ancelotti told the post-match news conference.
Fourth-placed Lyon host Toulouse on Sunday hoping to leapfrog St Etienne, who drew 0-0 at Valenciennes on Friday, into the third and final Champions League qualifying spot.
Stade Rennes slumped to a 4-2 loss at lowly Evian Thonon Gaillard ahead of next weekend's League Cup final against St Etienne.
Rennes, who were fourth in the standings after 22 games, have won only one league games since then, slipping to 10th on 42 points.
Former Arsenal forward Jeremie Aliadiere scored his 13th and 14th goals of the season as eighth-placed Lorient recovered from last weekend's 5-0 rout at Lille with a 4-1 home win over mid-table Bastia.
In Bordeaux, the ninth-placed hosts scored one more goal in a game than they have done in the last eight league matches when they defeated seventh-placed Montpellier 4-2.
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- Salvatore Sirigu