RABAT: Sloane Stephens won a marathon three-setter and top seed Martina Trevisan was forced to retire on Thursday in the quarterfinals of the Grand Prix Son Altesse Royale La Princesse Lalla Meryem in Rabat, Morocco. Stephens outlasted fellow American Peyton Stearns 6-7 (4), 6-3, 7-6 (6) in 2 hours and 46 minutes. Stephens overcame five double faults and saved 7 of 13 break points. She converted just 28 percent of her second serves. Trevisan was forced to retire in the second set with an injury. The Italian was down a set to Austrian Julia Grabher, who advances to the semifinals. In the other quarters, Italian Lucia Bronzetti defeated No. 4 Alycia Parks in straight sets and Julia Riera of Argentina rallied to beat sixth-seeded Yulia Putintseva of Kazakhstan, 5-7, 6-4, 6-2. Internationaux de Strasbourg: Frenchwoman Clara Burel upended No. 4 seed Bernarda Pera 6-2, 3-6, 6-4 in the quarterfinals in France. Burel had five aces and saved 11 of 16 break points to advance to the semifinals, where she’ll play Elina Svitolina of the Ukraine, a 6-3, 6-4 winner over No. 6 Varvara Gracheva of Russia. Seventh-seeded Lauren Davis rallied to defeat Russian Anastasia Pavlyuchenkova 1-6, 7-6 (2), 6-0 in 2 hours, 34 minutes. Davis will play Anna Blinkova in the semis; the Russian ousted American Emma Navarro 6-4, 6-4.