Sharapova, who won the title here in 2008 and has lost three finals — including last year's decider to
"Wow. I've won 600 matches?" Sharapova asked, responding to a question in an on-court interview. "Is this like a friendly reminder that I'm getting old? Might be."
The 28-year-old, five-time major winner is playing her 13th Australian Open since 2003 so she knew what to expect when she lost concentration in the second set despite being up and break and 30-love.
"You know you're in a Grand Slam environment, third round and against an opponent you haven't played … that's fired up and is not going to just give you the match and that's exactly what happened," she said. "I am quite happy that I was able to step up in the third set. That was very important."
The first set was over in 26 minutes, with Sharapova getting two service breaks and not facing a break point herself. She was broken twice in the second, when Davis came back hard and eventually won in the tiebreaker, despite conceding a key point after a 27-shot rally when she volleyed into the net, and covered her face with her hand.
Sharapova took a bathroom break before the third set and returned with more composure, making just five unforced errors and breaking Davis three times.
The fifth-seeded Sharapova will next play No. 12 Belinda Bencic, who won the opening match on Rod Laver Arena, 4-6, 6-2, 6-4, against Kateryna Bondarenko.
Nishikori reached the 2014
Returning to the fourth round at Melbourne Park for the fourth straight year was a confidence booster, and he said the right wrist "actually, it was OK."
"In the first set I was sore but after treatment I felt better," he said. "I tried to stay tough, concentrated again — I played better in last set."
There was a full house on Margaret Court Arena for the match, including a big section of Japanese supporters waving flags, while matches on uncovered outside courts were delayed because of rain. Seven doubles matches were later postponed.
No. 15 David Goffin beat No. 19 Dominic Thiem, 6-1, 3-6, 7-6 (2), 7-5 — his first win against a top-20 player at a Grand Slam — to reach the fourth round in Melbourne for the first time.
He faces a tougher proposition next, against either