"I'm a little disappointed," Williams said. "I don't think I played great, but I'm glad to have gotten through."
The victory preserves the potential for a matchup with her sister, Venus, in the semifinals. It would be the sister's 20th career meeting, with Venus up 10-9. The two-time defending champion is still alive to claim a record sixth tournament title, which would pass Steffi Graf.
"I'm always going to be up for V, because she's playing really well and always playing me super tough," Williams said. "I feel like playing her it's like I have to automatically be on a different level because she's already playing on a different level."
Li, ranked 40th, took control of the match quickly, taking the first five games against a sleepy Williams. Always the fighter, Williams stormed back to win the next four game, but Li claimed the first set. Li, 27, had Williams on the ropes several times in the second set. She had two break points that would have given her a 5-4 lead and another break point with the opportunity to go up 6-5, but she couldn't convert. She was 0-6 in break points in the second set.
"I mean, she was so strong on the court," Li said. "I have chances in the second set. I have like maybe six or seven breakpoint, but I didn't hold for one point. She just like - she didn't gave me any chance."
Williams took control in the second set tiebreaker as Li littered the purple court with six errors. From there she was on cruise control and a probably date with big sister, who plays Czech Iveta Benesova tonight.