American seventh seed Sloane Stephens beat the 19th-seeded Spaniard, Garbine Muguruza, 6-4, 6-3 to reach the quarter-finals of the French Open at Roland Garros in Paris. Stephens, who plays Briton Johanna Konta next, was the runner-up here last year while Muguruza won the tournament in 2016.