Wellington: Top seed Serena Williams overcame windy conditions to reach the semi-finals of the Auckland Classic on Friday with a 6-4 6-3 victory over Germany's Laura Siegemund.
The 23-times grand slam winner will meet either third seed Amanda Anisimova or Canada's Eugenie Bouchard in the last four.
Williams had little trouble against the 31-year-old German although the gusty breezes at Auckland Tennis Centre played havoc with her ball toss, especially when she was serving for the match at 5-3 in the second set.
She saved one break point, a characteristic of the match, in the final game but served an ace to get to match point then sealed it when a Siegemund forehand return went wide while she was under pressure.
"She was an incredibly tricky player," Williams said of the one hour, 28 minute match. "The conditions definitely didn't help so ... it's good to get through that."
Jessica Pegula was the first player to advance to the semi- finals when her opponent Alize Cornet retired in the second set.
The American had raced through the first set 6-0 and was leading 3-2 in the second before the Frenchwoman retired with a leg injury after an hour's play.
Pegula will meet either crowd favourite Caroline Wozniacki or two-time defending champion Julia Goerges in the semi-finals, with the pair due to play their quarter-final later on Friday.
Wozniacki and Williams are also scheduled to play their doubles semi-final against the Belgian pair of Kirsten Flipkens and Alison Van Uytvanck in the evening session.