For decades, hardly anyone knew the University of Denver even had a women's tennis team. But when coach Dana Young's charges unexpectedly won the Sun Belt Conference title last spring and earned an NCAA tournament berth, even the Williams sisters couldn't have caused a bigger stir on campus. The team's number-one singles player, then and now, is a steady blond slugger named Yanick Dullens from Susteren, Netherlands, who went 26-7 in matches last year and continues to lead the Pioneers, whose 8-2 mark this season promises another NCAA appearance. A senior who also plays number-one doubles, Dullens is 16-8 in singles matches and 20-9 in doubles this year.