0556 GMT October 20, 2019
France forward Gignac took his goal tally in the league this season to 19 when he pounced on a mistake by Metz goalkeeper Anthony Mfa in the 38th minute, Reuters reported.
The Gabon international dropped the ball following a right-wing corner and the Marseille striker swiveled sharply to hook the rebound low into the net.
Gignac then made it 2-0 in the 62nd minute when Dimitri Payet, who had a superb game in midfield, sent him racing clear and he waited for Mfa to rush out at his feet before carefully dinking the ball over the keeper's head.
Marcelo Bielsa's Marseille moved up to fourth in the table, on 60 points and with three games left to play, and back in with a strong chance of claiming the third place that offers a slot in the preliminary round of next season's Champions League.
Monaco, which is two points better off in third position, will host Toulouse on Sunday.
Paris St Germain, which is three points clear at the top, visits Nantes on Sunday.
Metz's defeat leaves the team with a mountain to climb to escape relegation. It is second from bottom, eight points from safety with three games to go.