MELBOURNE, Australia — Wimbledon champion Garbiñe Muguruza struggled with the heat and Hsieh Su-wei’s game before losing 7-6 (1), 6-4 on Thursday as the upsets intensified at the Australian Open. Muguruza, seeded third, follows Venus Williams and U.S. Open champion Sloane Stephens out of the tournament in the first week, leaving three major winners still in the women’s draw — and two could meet in the third round.