Serena Williams, chasing her first title in three years, wore down a tenacious Laura Siegemund on Friday to set up a semi-final showdown with Amanda Anisimova at the WTA Auckland Classic.
Siegemund had upset US teen prodigy Coco Gauff to reach the final eight and kept up the pressure until the first set hit 4-4, when Williams moved up a gear to win 6-4, 6-3 in just under 90 minutes.
The German claimed her own service break early in the second set but her opponent broke back to level at 3-3 and then commanded the next three games to take the match.
Although still troubled by the Auckland wind, Williams said she was determined to prove herself this week as she uses the competition to fine-tune ahead of the Australian Open.
"The conditions definitely didn't help, so it was good to get through that," she said.
Williams had her last tournament win at the 2017 Australian Open and before she arrived in Auckland she had not played since losing the US Open final last September.
But she is now in the semi-finals of both the singles and doubles in Auckland and said the court time was beneficial in her bid to win a 24th Grand Slam in Australia later in the month.
"The body's feeling great. I said I wanted to play singles and doubles here so I knew what I was going to be up against and I'm happy to still be in the tournament," she said.
Anisimova, the tournament third seed and rising star of American tennis, won an error-strewn three-set joust with Canada's Eugenie Bouchard to achieve her "lifelong dream" of playing Williams.
"I said before the tournament in an interview that my biggest wish is to play her before she retires so this is the happiest I've ever been," she said.
She and Bouchard survived on service breaks throughout their close encounter, converting 13 of 30 break points before the 18-year-old Anisimova eventually won 6-2, 3-6, 6-4.
Former World number one Caroline Wozniacki overcame defending champion and fourth seed Julia Goerges 6-1, 6-4 to also make the final four and a semi-final clash with unheralded American Jessica Pegula.
Pegula, who is yet to face a seeded opponent in the tournament, was up 6-0, 3-2 against Alize Cornet when the Frenchwoman retired hurt with a thigh injury.