KEY BISCAYNE, Fla. (AP) — 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.