Agnieszka Radwanska

Stephens, Venus advance to Miami Open quarterfinals

Sloane Stephens' loudest fan kept shouting advice and encouragement from the upper deck Monday, perhaps providing the nudge she needed to shake a post- U.S. Open slump.

Stephens earned her biggest victory since winning last year's Open, beating No. 3-ranked Garbine Muguruza 6-3, 6-4 Monday to reach the quarterfinals at the Miami Open.

"Keep it in the court, girl — that's all you've got to do!" the spectator hollered, and Stephens did. During a post-match on-court interview, Stephens thanked the fan, who has attended her past two matches.

"I have no idea who that is," she said later. "Day before yesterday was the first time I'd ever seen...