Second-placed OM trail leaders PSG by nine points, with a vastly inferior goal difference and four games left. A win against Bastia would delay their arch rivals' coronation as champions even if PSG beat Valenciennes on Sunday.
Once again, Marseille will rely primarily on their sturdy defence.
They have not conceded a goal in their last seven league matches and have won 12 of their games by 1-0, equalling PSG's record from 2003/04.
"We have turned the screw," fullback Rod Fanni, who is doubtful because of an ankle injury, told the club's website.
"Let's hope we will continue to hang in there because we have been suffering this year but it has been worth it."
"Not over yet but we'll need an almighty collapse in Paris," OM midfielder Joey Barton said on his Twitter feed.
PSG, whose Qatari investors have poured more than 200 million euros into transfers since they took over two years ago, will have a midfield problem against Valenciennes, however.
Italy international Thiago Motta is on a three-match ban while Marco Verratti and David Beckham will also be suspended after picking up red cards in the previous game at Evian Thonon Gaillard.
The PSG players are impatient to win the club's third league title, after 1986 and 1994.
"We need a victory, which we hope to clinch on Sunday so we can be champions at home," Argentine midfielder Javier Pastore told the club's website.
Third-placed Olympique Lyon are on 60 points, four adrift of OM, and, with the title out of their reach, will probably focus more on Saint-Etienne's game against Girondins Bordeaux on Friday.
Fourth-placed Saint-Etienne, on 58 points, will leapfrog them into third if they win as Lyon play on Sunday at Nancy, who left the relegation zone last month for the first time since September.
The top two teams in Ligue 1 qualify for the Champions League group stage while the third-placed team go into a preliminary round.
Nancy, who reached the December break with 11 points, now have 35 and sit in 16th place one point above the relegation zone.
"If we manage to stay up, which is not done yet, we will leave the Marcel Picot stadium by bicycle and climb the Col de la Schlucht [at the end of a 120-km ride]," president Jacques Rousselot told Reuters.
Bottom club Troyes will face almost certain relegation if they fail to beat 17th-placed Evian Thonon Gaillard on Saturday.
