Williams was an interested spectator on the players balcony during Wozniacki's win, but the Dane missed the American's heroics on Tuesday night, as she was in a restaurant celebrating her father (and coach) Piotr's birthday.
"I know how she is playing, and she has been playing well, apparently, so I know she is ready," said Wozniacki of Williams. "Let's hope we both get there."
Wozniacki gave herself a pass mark today against Siegemund, who got her first round berth as a "lucky loser" out of qualifying.
The Dane was mostly untroubled in the first set, but had to fight hard in the second, as Siegemund took a more aggressive approach and showed some lovely touches at the net.
The German fought back, breaking the world No3's serve, before Wozniacki accelerated away again.
"It wasn't the prettiest match I've played," said the 28-year-old. "I was just trying to get back into the rhythm. I have been practising really well so I am hoping every match is going to be better.
"I never expect much playing-wise in the first match because you are a little rusty and have to get back into it.
"All I can expect from myself is that I fight well and I try my hardest. I served well in periods, I mixed up the pace well in periods, you have to look at the positives."
If Wozniacki is to make another run at the title, she'll face five matches in consecutive days, a tougher schedule than many of her opponents, some of whom started on Monday and have had rest days between rounds.
"I'm okay, I'm ready for it," said Wozniacki. "I've been working hard fitness-wise. Obviously it is different when you are in a match."
Wozniacki faces Canadian qualifier Bianca Andreescu tomorrow. The 18-year-old is ranked world No152, but has come through four matches in Auckland.
Others to progress today included Spain's Sara Sorribes Tormo who outlasted Auckland regular and seventh seed Kirsten Flipkens (Belgium) 6-4, 1-6, 6-1, while third seed Su-Wei Hsieh (Taiwan) displayed all facets of her unique style to beat an erratic Monica Puig 6-1, 7-6(3).
Kiwi Paige Hourigan thrilled local fans as she won through to the doubles semifinals alongside American Taylor Townsend.
The pair had never played together before this week, but managed an impressive fightback against the experienced Australian combination of Monique Adamczak and Jessica Moore to prevail 3-6, 6-1, 10-8.
"Taylor kept on telling me just believe in myself, to keep on moving forward, fight for every point and be positive," said Hourigan.
"She was playing great the whole match and I just managed to stay solid and set her up and she was able to finish at the net."
