Media and photographers quickly filled the stands, and the players' lounge emptied, with players and their coaches taking photos and videos of the 38-time major winner (22 in singles) from their balcony.
A security guard was stationed metres from Williams - with two others watching over the court - while tournament officials and volunteers stopped to take in the scene.
"It's hard to imagine just how big Serena is globally," said ASB Classic tournament director Karl Budge, who had an good insight with his previous role working for the WTA tour.
"There are not many who match her. She is one of the few people where you could go just about anywhere in the world and she is recognised by her first name only.
"For 15 years in a row she has made the lists of the 100 biggest celebrities on the planet and there is a decent argument that if she was a male, she might be ranked as the greatest athlete of all time.
"That's how good she is."
The first taste of Williams on court yesterday didn't disappoint.
She hit with her trademark power, pushing her hitting partner to the limit with some huge groundstrokes off both wings.
With her coach and physio watching on, Williams trained for almost two hours, despite only arriving in New Zealand six hours earlier.
Sister Venus briefly interrupted - probably the only person on the planet who could - to come and say hello midway through the session, but otherwise it was all business, with Williams demonstrating the work ethic that has seen her win more than 71 WTA tournaments, and hold the No1 ranking for more than 300 weeks.
Williams is here with a large entourage, including her coach Patrick Mouratoglou, hitting partner, physiotherapist and business manager. A representative from her team also arrived in Auckland on Thursday, checking the venue and facilities and doing a sweep of the hotel and player areas at the stadium.
"She's very focused," said Budge. "She wants to win the Australian Open and has decided Auckland will be a good preparation for that.
"That is why she's here."
Williams arrived yesterday morning just after 6am, alongside good friend Caroline Wozniacki. She was quickly whisked to waiting transport, but briefly spoke to reporters, confirming the influence of Venus in her decision to come here.
"It was all Venus so we should just thank Venus whenever she arrives," said Williams, when asked about coming to Auckland for the first time. "She said it was great and I should come so I always listen to big sister."
Williams will visit Auckland's west coast beaches by helicopter today before a charity exhibition doubles match tomorrow.
"It's always fun to go places you have never been, so I'm excited to be here," said Serena.
And Auckland, it seems, is thrilled to have her.
