PARIS, April 6 (Reuters) - Two goals in two minutes from Djibril Cisse and Mamadou Niang helped Olympique Marseille defeat Ligue 1 leaders Olympique Lyon 3-1 on Sunday. It was Marseille's first victory at the Stade Velodrome over the six times French champions since September 1997. Marseille, who won 2-1 at Lyon earlier this season, also became the first side in this campaign to pick up six points against Lyon. Cisse and Niang scored in the 26th and 28th minute shooting home backpasses which caught Lyon's keeper Gregory Coupet off balance. Lyon, who were on a run of six wins, got back into the game through an own goal from Marseille captain Lorik Cana, who misheaded Juninho's long-range free kick in the dying seconds of the first half. Despite having to replace injured defensive midfielder Jeremy Toulalan and striker Fred by Kim Kallstrom and Hatem Ben Arfa in the 11th and 31st minute, the French champions stepped up a gear in the second half. Niang sealed his team's victory when he headed home a Benoit Cheyrou centre in the 54th minute. With six matches left, the result cut Lyon's lead to six points over Girondins Bordeaux, who won 2-0 at Stade Rennes on Saturday. Marseille stay fourth three points adrift of AS Nancy who kept the ticket to the Champions League qualifying round with a 1-0 home win over relegation-threatened Paris St Germain earlier on Sunday. Nancy's winning goal was scored by Marc-Antoine Fortune who headed home in the 69th minute shortly after PSG had an effort controversially disallowed for offside after a one-two between Pedro Pauleta and Amana Diane. The defeat puts PSG back into the drop zone. They are 18th, level on 35 points with Racing Lens, Toulouse and Strasbourg, although above the latter on goal difference. Bottom club Metz have just 18 points and are certain to be relegated.