United States' Serena Williams makes a forehand return to compatriot Danielle Collins during a tuneup event ahead of the Australian Open tennis championships in Melbourne, Australia, Friday, Feb. 5, 2021. (AP Photo/Andy Brownbill)MELBOURNE – Serena Williams withdrew from an Australian Open tuneup tournament citing a right shoulder injury on Friday within hours of setting up a semifinal match against top-ranked Ash Barty. Garbine Muguruza beat defending Australian Open champion Sofia Kenin 6-2, 6-2 to advance to the semifinals, reversing their result of their 2020 final at Melbourne Park. On either side of a delay on outside courts because of rain, former Wimbledon, U.S. Open and Australian champion Angelique Kerber beat No. 4 Borna Coric out in the quarterfinals after wins over Australian players earlier in the day.