Williams won despite an unreliable serve, a poor second set and 51 unforced errors. (Source: Reuters)

Serena Williams abused her racket, scolded herself and even made angry faces at the sun.

In the end, as usual, she took out her frustration on the ball.

The seven-time Key Biscayne champion overcame her annoyance and shaky play Wednesday for her 700th career victory, beating Sabine Lisicki 7-6 (4), 1-6, 6-3 to reach the semifinals of the Miami Open.

Williams won despite an unreliable serve, a poor second set and 51 unforced errors. She looked flatfooted and listless at times, and seemed especially vexed when playing on the side looking into the sun.

“It’s always tough on that side,” she said. “You just don’t see. You just have to adjust.”

She did, earning her 16th consecutive victory on Key Biscayne, where she’s the two-time defending champion.

“I know today wasn’t my best day,” she said. “I just told myself, I’m not serving the way I normally serve and hitting the way I normally would hit, so at this point all I can do is just fight and try to give 200 percent instead of 100 percent.”

The No. 1-seeded Williams’ opponent Thursday night will be No. 3 Simona Halep, who beat unseeded American Sloane Stephens 6-1, 7-5. No. 9 Andrea Petkovic plays No. 12 Carla Suarez Navarro in the other semifinal.

Two-time champion Andy Murray advanced to the men’s semifinals by rallying past unseeded Dominic Thiem 3-6, 6-4, 6-1. Murray’s opponent Friday will be No. 8 Tomas Berdych, who beat unseeded Juan Monaco 6-3, 6-4.

Williams improved her career record to 700-120, making her the eighth woman in the Open Era to reach the milestone. She was presented with a cake on the court, similar to the honor Murray received following his 500th victory Tuesday.

“I think my destiny was to play tennis,” Williams said. “I saw a picture where I was in a stroller on the tennis court.”

The No. 1-seeded Williams withdrew before the Indian Wells semifinal earlier this month with a right knee injury. She had been scheduled to play Halep, who went on to win the title and leads the women’s tour with 24 victories this year.

“I was really disappointed to not be able to play and just not even be close to 100 percent,” Williams said. “So I look forward to it this time. I’m just happy to be in the semis and still be alive somehow.”

“It will be a very nice match,” Halep said. “I have to try everything. She is No. 1 in the world. She’s the best player. I have nothing to lose.”

For much of Williams’ quarterfinal, she trailed Lisicki in fist pumps and points, and let frustration quickly show.

After losing three consecutive games to fall behind 4-3 in the first set, the Floridian pounded the court with her racket and drew jeers in the stadium she considers her home court.

Williams won the first set only because Lisicki wobbled in the tiebreaker, hitting three shots into the net before double-faulting on the final point.

Williams played even worse in the second set, losing six games in a row, but then began to grunt louder and hit harder, with positive results. She earned the only break of the final set in the second game and held from there, serving out the match at love.

“Come on!” she shouted when it ended, as if already gearing up for the semifinal.

Tournament officials then rolled out the cake, with pink, green and purple frosting. What’s her favorite kind?

“Vanilla,” she said.

It wasn’t really Williams’ day, but she won anyway.