Williams came out with a solid straight sets performance against Laura Siegemund of Germany, winning the match 6-4, 6-3 in an hour and a half. The 23-time Grand Slam winner struck 26 winners to Siegemund's 20, and outpaced her six aces to one.
"It was good for me to just fight, you know," Serena was quoted as saying by WTA after her win. "She has a really good game, and she stepped up and hit a lot of good winners, so it wasn't really easy. I just had to step up and play a little better, and hopefully get through it.
On the other hand, Wozniacki handed Julia Goerges her first loss at the ASB Classic in three years. The former World No.1 overcame the two-time defending champion and No.5 seed, 6-1, 6-4, to advance to the last four.
"I've had so many tough matches against Julia in the past, and I knew this one was going to be tough as well," Wozniacki said after the match.
"She has a big serve and big shots, so I needed to be ready for every point. I've been serving really well this week, so I hope it can continue."
She will next face American Jessica Pegula, after she advanced past Alize Cornet via a retirement.
( With inputs from IANS )