PARIS, April 6 (Reuters) - A diving header by Marc-Antoine Fortune helped AS Nancy stay in the hunt for a place in the Champions League qualifying round with a 1-0 home win over relegation-threatened Paris St Germain on Sunday. The 26-year-old striker scored 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 win cements Nancy in third place, six points ahead of Olympique Marseille, who host six times champions Olympique Lyon later on Sunday. Lyon top the table with a lead of six points over Girondins Bordeaux, who won 2-0 at Stade Rennes on Saturday, and 12 over Nancy. 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 on the verge of going down.