Keothavong has set her sights on a place in the world's top 50
British number one Anne Keothavong continued her fine start to the year with an impressive victory over eighth seed Carla Suarez Navarro in Auckland.
The 25-year-old followed up her first-round win over Mirjana Lucic with a 6-2 6-4 defeat of Spaniard Suarez Navarro.
Keothavong will face Ayumi Morita in the last eight after the Japanese qualifier upset fourth seed Aleksandra Wozniak 7-5 6-2.
Top seeds Elena Dementieva and Caroline Wozniacki both made the quarter-finals.
Russian Dementieva beat New Zealand's Marina Erakovic 6-2 6-3, while Denmark's Wozniacki saw off American Jill Craybas 6-4 7-5.
Edina Gallovits of Romania had a surprise 6-3 6-3 win over Spanish third seed Anabel Medina Garrigues and Russia's Elena Vesnina beat sixth seed Nicole Vaidisova of the Czech Republic 6-4 6-3.
I'm not sure I agree with the on-court coaching that is now allowed
Keothavong is currently at a career-high ranking of 60 and has set herself an immediate target of a place in the world's top 50.
Victory over Suarez Navarro, the world number 46, will help her towards that aim and she next faces the 83rd-ranked Morita on Thursday.
The pair have met once before, with Keothavong beating the 18-year-old in straight sets in qualifying for the 2007 French Open.
"I'm really pleased to get through another match here in Auckland against a higher-ranked opponent," the Londoner told her website.
"I felt I was the more aggressive player today in tricky conditions. The wind picked up towards the end of the first set and there were several breaks of serve in the second set.
"I'm not sure I agree with the on-court coaching that is now allowed at WTA tournaments but I made use of it and got my coach Nigel Sears to run on court for his daily bit of exercise. He assured me that what I was trying to do was right.
"Tomorrow's match will be completely different to today's. I've played Morita before but she's obviously got better with each match here and is playing with a lot of confidence.
"I just need to stay focused on myself and what I have to do and hopefully the result will take care of itself."