Teenager Andy Murray is poised to be confirmed as the new British number one after beating South Africa's Rik de Voest in Memphis.
Murray has extended his winning streak to seven matches
The result, coupled with Tim Henman's defeat in Rotterdam, will move Murray ahead of Henman and Greg Rusedski when the rankings are published on Monday.
Murray was made to work hard for his three-set victory over the lucky loser.
The 18-year-old swept to a dominant early lead, but was pegged back before finally prevailing 7-6 (7-4) 3-6 7-5.
De Voest only made the main draw when Nicolas Kiefer withdrew but took advantage by beating Jonas Bjorkman.
Murray looked to be in a different class as he raced to a 4-0 lead but he found De Voest hard to shake off.
He needed a tie-break in the first set and dropped the second before beating the world number 149 to reach the last eight, his seventh straight win.
As the rankings stand on Friday, Murray is 47th, Rusedski 43rd and Henman 40th, but results this week - Rusedski lost in the second round in Rotterdam - will see that change on Monday.
Henman has been Britain's number one since 1999, but Murray's form over the last 12 months has finally ended his reign.
Murray, who won his maiden ATP Tour title in San Jose last week, said he was reaping the rewards of his hard work to develop his fitness.
His impressive performance at Wimbledon last year was undermined by fitness problems, especially against David Nalbandian, but there was no sign of a repeat in Memphis.
"I feel much fitter and stronger now," said Murray.
"There was a lot of questions about my fitness last year. I got tired in my match at Wimbledon.
"I thought I was the fresher of the two at the end of the match (against De Voest). I feel quite good having come through five matches at San Jose and won in three sets on Thursday."
Murray will play Robin Soderling in the quarter-finals - the man he beat at the same stage in San Jose last week.
"I suppose in some ways it's a good thing because you know what their weaknesses are and you kind of know what to expect," said Murray.
"You have to change things because if you do exactly the same as you did in the last match it's going to be a bit predictable.
"So you need to have a few surprise tactics and I'll talk to my coach about that and I'm sure I'll be able to do it."