The 45-year-old put up a superb show before losing 6-4 4-6 6-2 to the No.52-ranked Linette, who was only two years old when Williams played her first professional singles match.
Tuesday's match was Williams' 1,101st in singles on the WTA Tour. But the competitiveness she showed against a player 12 years her junior will give her confidence as she heads to Australia for the Hobart International and the Australian Open.
The seven-time major champion received wild-card entries into the Auckland tournament and also in Hobart from January 12 and at the first grand slam tournament of the year at Melbourne Park.
The Auckland match was Williams' first since she lost 6-3 2-6 6-1 to Karolina Muchova in the first round of the US Open last August. She played only three tournaments in 2025, beating Peyton Stearns in July to become the second-oldest woman - behind Martina Navratilova - to win a match on the WTA Tour.
Williams appeared fit, moved freely, served seven aces and hit hard on both sides.
"Look at the level she brought. She moved really great," Linette said in a courtside TV interview. "She was really hitting well, especially when she was running to the open space.
"It was really impressive and I really had to stay calm. She pushes you to a spot you don't want to be and that's where I was for a while, so I'm really glad I was able to refresh and come back with a little bit better game."
Williams, ranked No.582 this week, has been a regular visitor to Auckland in the latter part of her career. She beat Caroline Wozniacki in the 2015 final for the 41st of her 46 WTA Tour titles. This year, she told reporters, she didn't feel any pressure.
"The biggest pressure is the one we put on ourselves, right?" Williams said. "And then when you look back and you're like, 'it wasn't such a big deal.'
"So hopefully I can look back with the 20/20 vision while I'm in the present, like just let it go, let it flow, enjoy it and be in the moment. That's not easy to do and that's why people love sports, right?"
Williams started strongly and had her first ace in her opening service game. She was broken by Linette in the fifth game and trailed 5-2 before breaking back. Linette took the first set in 51 minutes.
In the second set, Williams broke in the sixth and 10th games. She hit hard to the corners, then was able pull out sharp winners down the line. She also went to the net effectively.
Linette broke decisively in the fifth game of the third set.
Top-seeded Elina Svitolina beat Vavara Gracheva 6-3 6-1 on Tuesday in her first singles match since she took a break from the tour in September for mental health reasons.
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