Sabalenka remains unbeaten this year

Australian Open champion Aryna Sabalenka improved to 13-0 this year with a 2-6, 6-1, 6-1 victory over Jelena Ostapenko to reach the quarterfinals of the Dubai Championships.

The second-ranked Sabalenka will next face Barbora Krejcikova, who beat fellow Czech player Petra Kvitova 6-3, 6-2.

Earlier, top-ranked Iga Swiatek reached the quarterfinals by beating Liudmila Samsonova 6-1, 6-0.

The 21-year-old Pole was then issued a walkover to the semifinals after former No. 1 Karolina Pliskova withdrew because of an illness. Pliskova had advanced to the quarterfinals by defeating Anhelina Kalinina 7-5, 6-7 (6), 6-2 in the round of 16.

Swiatek, a three-time Grand Slam champion, has won her last five matches including the successful defense of her Qatar Open title last week.

Swiatek will face the winner of the all-american quarterfinal match between Madison Keys and Coco Gauff.

Keys beat Victoria Azarenka 6-2, 6-1, and the 18-year-old Gauff advanced after Australian Open runner-up Elena Rybakina withdrew from their scheduled match because of a lower back injury.

• Thomas Bellucci, Brazil’s main flagbearer on the men’s tennis tour for the last decade, has retired after losing in straight sets to sixth-seeded Sebastian Baez 6-3, 6-2 in the first round of the Rio Open.

Belluci is now preparing to transition into coaching.

The 35-year-old Bellucci won 200 professional matches, lifted four titles and reached a career-high No. 21 in the ATP rankings. He’s one of the five players to win a set 6-0 against Novak Djokovic on clay. He beat Top 10 players six times in his career, including then No. 4-ranked Andy Murray at the Madrid Open in 2011.