"That's all right,'' Richard Williams told his daughter with a nod of encouragement.
It was all the coaching Serena needed. Her shots began to land inside the lines, and the top-ranked Williams overcame a dismal start Wednesday to beat Li Na 4-6, 7-6 (1), 6-2 in the quarterfinals of the Sony Ericsson Open.
Williams awaited a possible semifinal showdown Thursday against her sister Venus, who was to face No. 26-seeded Iveta Benesova on Wednesday night. The other semifinal will be between No. 8-seeded Svetlana Kuznetsova and No. 11 Victoria Azarenka.
No. 3 Novak Djokovic became the first men's semifinalist by beating No. 10 Jo-Wilfried Tsonga 6-3, 6-4. Djokovic won the title in 2007.
The Williams sisters have dominated the tournament for more than a decade. Venus is a three-time champion, while Serena seeks her sixth title, which would break the record she shares with Steffi Graf.
Li nearly ended Serena's Key Biscayne reign. At the start Williams looked lethargic in the 80-degree sunshine, and several times she declined to chase shot that seemed within reach.
"Wake up!'' one spectator shouted.
"Maybe I was tired, but that's still not an excuse really,'' Serena said. "I definitely wasn't moving my feet at all. I just wasn't doing anything that made a lot of sense at all.''
When the score reached 5-love, Richard Williams left his seat in the stands and positioned himself courtside near the baseline. He's the sisters' coach as well as their dad, and while he said little, he lifted Serena's spirits.
"I just felt like he was there really supporting, and I felt the support more when he was up close as opposed to in the stands,'' she said. "I just felt like I could take it up to another level.''
She did, moving better and punctuating her shots with more emphatic grunts as the match slowly swung her way. There were no service breaks in the second set, but the unseeded Li failed to convert six break-point chances. The last came at 5-all, and Williams erased it with a service winner.
Li made things easy for Williams in the tiebreaker by committing six unforced errors. As the third set began to slip away from Li, she vented her frustration by slamming a ball against the backstop on the far end of the court.
"I gave her the tiebreak,'' Li said. "I couldn't focus in the final set. After she won the second set, I didn't think I had a chance.''
Li double-faulted on break point to fall behind 2-1, part of a stretch where Williams won 16 points in a row en route to a 5-1 lead. Williams closed out the victory with a service winner.
"The whole match is still an F,'' she said. "I'm glad to have gotten through.''
It was part of a familiar pattern of inconsistency for Williams, who has managed the curious feat of reaching the semifinals despite losing five consecutive games three times in her past two matches.
"I need to be more consistent in my play,'' she said. "I don't have to be out there going three sets. That's what I think it tells me more than anything.''
She improved her record at Key Biscayne to 51-5, with one loss since 2001 - to her sister.
