Stacelita just keeps getting better and better. In a performance that recalled the daring exploits last year of Zarkava, she remained undefeated with an impressive four-length victory in the $1.1 million Prix de Diane (French Oaks) at Chantilly on Sunday, in the process giving her trainer, Jean-Claude Rouget, his 11th group race triumph of the year.\nPerfectly placed by Christophe Lemaire in the early going, Stacelita cruised to the lead at the top of the stretch, three furlongs from home. A French-bred daughter of the German stallion Monsun, Stacelita drew off for a handy score over her Rouget-trained stablemate and French 1000 Guineas runner-up, Tamazirte, with Plumania third, a half-length further back. The time for the 1 5/16 miles on good to soft ground was 2:06.23.\nPreviously the six-length winner of the 1 1/4-mile Group 1 Prix Saint-Alary at Longchamp, Stacelita is now a perfect 5 for 5, her combined margin of victory an astonishing 18 lengths. Owned by Martin Schwartz and Ecurie Monastic and bred by Jean-Pierre Dubois, she will be given the summer off with Longchamp's Prix Vermeille on Sept. 13 scheduled as her prep for the Oct. 3 Prix de l'Arc de Triomphe, for which she is now the 7-1 second favorite with both Ladbrokes and William Hill behind the 4-1 Epsom Derby winner, Sea the Stars.