Watson came through three qualifying matches in Auckland
British teenager Heather Watson reached her first WTA Tour quarter-final with a 7-6 (7-5) 6-1 win over ninth seed Carla Suarez Navarro at the Auckland Classic.
The 18-year-old from Guernsey continued her superb start to the year with a fifth consecutive victory after coming through qualifying.
Watson will next face Shuai Peng after the Chinese player beat third seed Svetlana Kuznetsova 2-6 6-4 6-4.
British number two Anne Keothavong lost 7-5 6-3 to Kateryna Bondarenko.
"Super windy this afternoon and my opponent kept it together better," Keothavong said on Twitter. "Not a happy bunny but I'll get over it."
Top seeds Maria Sharapova and Yanina Wickmayer advanced with wins over Renata Voracova (6-3 7-5) and Sabine Lisicki (6-2 3-6 6-2) respectively.
Watson's previous best effort at a WTA event came in Eastbourne last year when she made it through qualifying to reach the last 16.
I'm loving the New Year so far and the off-season training is definitely paying off
But she improved on that performance with victory over Spain's Suarez Navarro, ranked 119 places higher at 57 in the world, and Watson is now projected to enter the top 150 on Monday for the first time.
The Briton battled through a tight opening set in the tie-break after dropping serve three times and went on to dominate the second set.
Watson will play Peng, the world number 72, on Thursday for a place in the semi-finals against defending champion Wickmayer or Simona Halep.
"I'm loving the New Year so far and the off-season training is definitely paying off," Watson told
the LTA website.
"I'm definitely very happy with my performances so far in the tournament and I just want to continue getting better, stronger and smarter as a player. I can't wait for my next match."
Kuznetsova, down to 27th in the rankings, will head to Sydney after failing to kick off the year with the boost she had been looking for.
"I was leading all the time but when you don't take chances, the opponent will take them," she said. "She played great today but I had so many possibilities."
Sharapova admitted her performance against Voracova had been "sloppy", with the gusty conditions playing a part.
"With the wind my ball toss was all over the place," said the Russian. "That's something I'll have to work on in my next game.
"I played a really tough opponent today. She was very different from my first opponent, very flat and deep and it was difficult to find my rhythm."