AUCKLAND, New Zealand (AP) -- Qualifier John Isner upset fellow American Robby Ginepri 6-5, 6-7 (1), 7-6 (5) on Wednesday to reach the quarterfinals at the Heineken Open.
The match, which lasted 2 hours, 23 minutes, was Isner's fifth at the tournament after he played through three rounds of qualifying to reach the main draw. Four of those matches have gone to three sets.
Isner fired 17 aces in 17 service games, bringing his total in his past two matches to 29.
The 144th-ranked Isner saved nine of 11 break points and converted three of five to clinch his first meeting with the No. 47 Ginepri.
Earlier, sixth-seeded American Sam Querrey beat qualifier Gilles Muller of Luxembourg 3-6, 6-3, 6-4 to earn a spot in the quarterfinals.
Querrey, who also relied on a heavy serve, had nine aces but was disappointed in a lack of precision in other parts of his game.
"I served really well and played well on the break points, but I didn't volley that well and got a little bit frustrated,'' Querrey said.
"I usually don't mind playing similar players, but I find it a bit difficult against lefties because of the way the serve swings.''
Top-seeded Argentine Juan Martin Del Potro overcame a rusty start in his first match of 2009 to beat Ernests Gulbis of Latvia 4-6, 6-4, 6-1.
Del Potro, who soared up the rankings in 2008 and is currently No. 9, was handed a bye to the second round and struggled to find his rhythm in hot conditions before settling in to beat the No. 51-ranked Gulbis.
Defending champion Philipp Kohlschreiber of Germany also advanced to the quarterfinals, beating former No. 1 Juan Carlos Ferrero 6-4, 4-6, 7-6 (5).
Second-seeded David Ferrer of Spain beat Marc Gicquel of France, 6-7 (3), 6-4, 6-4 and third-seeded Robin Soderling of Sweden downed American qualifier Bobby Reynolds 6-3, 4-6, 6-2.