By Ian Westbrook
BBC Sport at Wimbledon
Maria Sharapova was given a real battle before seeing off the experienced Amy Frazier 6-4 7-5 and reaching her first Grand Slam quarter-final.
Sharapova won five games in a row to take the first set and go 1-0 up in the second before starting to look nervous.
Frazier broke to lead 5-4 but problems with her serve cost her dear.
In all, the American served 12 double faults and paid for it as the Russian, seeded 13th, wrapped up an impressive victory.
"I was very relieved as she beat the second seed (Ana Myskina), a French Open champion, and must be in good form which really showed against me," said Sharapova.
"She played a great match and made me work for it until the last point."
Sharapova takes on Ai Sugiyama next after a straight-sets win for the Japanese number one over Thailand's Tamarine Tanasugarn out on Court 13.
The 11th seed sealed her first quarter-final place in 12 appearances at Wimbledon with a 6-3 7-5 victory, which she concluded in one hour and 41 minutes.
"I've never played her before so can't predict what will happen but I'm looking forward to a very tough match," said Sharapova.