The No.3-seeded Williams was the first of the pair to move through, blasting 10 aces and needing just 52 minutes to get a little bit of family revenge on Jana Cepelova, 6-1, 6-0. Cepelova had beaten Serena Williams at the Family Circle Cup in Charleston last year - this one was no contest though.
This is Williams' second time playing the ASB Classic, going all the way to the final here a year ago before falling in three grueling sets to Ana Ivanovic. It would propel the American to her best season since 2010, winning the Dubai title and reaching another two finals in Montréal and Québec City.
"I felt very welcome when I came back on the court today - it was like I picked up where I left off last year," Williams said afterwards. "The fans appreciate every point here. They're very appreciative of all the effort the players give. And that feels good when you don't hit the best shot out there!
"But it went well for me today. To get to the final I'll have to play five days in a row, so I definitely don't want to play super long matches. It's much easier on me to play shorter matches like this."
Wozniacki, the No.1 seed, had a slightly tougher challenge in the feature evening match but still managed to move through relatively unscathed, outdoing Israeli qualifier Julia Glushko, 6-3, 6-2.
"Maybe it wasn't the prettiest match, but I got through and I won it," Wozniacki commented. "The first match is always tough. I served well, but I want to keep playing better as the week goes on.
"I love the crowd here, though. They made me feel very welcome. I love everybody here."
This is Wozniacki's second time playing the ASB Classic too - she was a quarterfinalist in 2009 - and during a pre-tournament shopping trip the Dane talked about how glad she is to be back here.
"I love it here," Wozniacki commented. "I haven't been back to Auckland for many years, but it's such a great place to start the season, and I'm excited to play and get the 2015 season going here."
There were mixed results for the other two seeds in action, with No.5 seed Svetlana Kuznetsova falling to Czech qualifier Lucie Hradecka in a two-hour-and-25-minute grinder, 3-6, 7-6(6), 6-4, but No.7 seed CoCo Vandeweghe dropping 11 aces en route to a 5-7, 6-2, 6-3 victory over Roberta Vinci.