Serena Williams makes quarterfinals of Collector Swedish Open Simona Halepm shown at the 2011 U.S. Open, retired in the third set of her match Thursday at the Collector Swedish Open. It was just the second loss in her last 18 matches. BASTAD, Sweden, July 18 (UPI) -- World No. 1 Serena Williams eased into the quarterfinals of the Collector Swedish Open but second-seeded Simona Halep is out after a retirement. Williams had little trouble in getting past Anna Tatishvili 6-2, 6-3 in 61 minutes. Williams, despite dropping serve three times, won 60 percent of the points when serving and 63 percent off Tatishvili's serve. Halep had won 17 of her last 18 matches since the middle of June, picking up her first three WTA titles in the process. But the schedule's pace seemed to take its toll Thursday as she retired Thursday after falling behind Flavia Pennetta 4-6, 7-5, 2-0. Qualifier Richel Hogenkamp ousted sixth-seeded Lesia Tsurenko 6-1, 2-6, 6-3 by converting five of her six break chances and Mathilde Johansson stopped Andrea Gamiz 7-5, 6-2 in the final second-round match. Williams draws fifth-seeded Lourdes Dominguez Lino in Friday's quarterfinals with Hogenkamp playing No. 3-seeded Klara Zakopalova in the other match in that half of the draw. Also Friday, eighth-seeded Johanna Larsson goes against Johansson and Pennetta faces Virginie Razzano.