Juan Martin del Potro beat another seeded player in the BNP Paribas Open, defeating No. 32 Philipp Kohlschreiber 7-6 (3), 7-6 (7) in the fourth round on Wednesday.
Del Potro, from Argentina, improved his match record to 17-4 this year as he rebounds from an injury-marred 2010. He has surged from No. 484 to 90th in the world rankings in a three-week span, winning a title at Delray Beach, Florida, and reaching the semifinals in two other tournaments.
"I am playing better than two months ago. I know it's a long road, but I'm still improving my serve, my forehand," he said. "It's very tough to play every day against these kind of players, and I need time to feel 100 percent again."
Now, Del Potro is into the quarterfinals, where he will play 25th-seeded Tommy Robredo of Spain. Robredo beat 21st-seeded American Sam Querrey 6-1, 6-3.
"I'm playing better match by match, and I don't know if I can play better than today," Del Potro said. "I just want to work hard. I need time to do it. I'm very patient."
Earlier in the tournament, Del Potro beat defending champion and No. 14 seed Ivan Ljubicic and No. 20 Alexandr Dolgopolov of Ukraine.
The world's top two players will be in action at night. No. 1 Rafael Nadal plays qualifier Somdev Devvarman, the first Indian to reach the fourth round.
No. 2 Roger Federer, a three-time champion at Indian Wells, plays wild card Ryan Harrison. Federer is 16-2 this year, while the 18-year-old American tries to beat a top-10 player for the first time, having lost two other meetings.
Robredo was hobbled by a leg problem at 2-2 in the second set in his match against Querrey. He first got treatment on his leg two weeks ago.
"I felt something there and then it was very tough for me to play," he said. "Luckily, I could win. I have one day to recover and hopefully I can go through."
Against Kohlschreiber, Del Potro called for a trainer in the middle of the first set.
"It was really hot and I play many, many matches, so I getting tired," he said, "but the people tell me to fight all the match, and that's what I did."
Del Potro rallied after trailing 6-1 in the second-set tiebreak, and won with an ace on his third match point.
No. 15 Marion Bartoli, the highest seeded woman in action Wednesday, ended Ana Ivanovic's run with a 6-4, 7-6 (4) quarterfinal victory. Ivanovic hadn't dropped a set until her loss.
Bartoli advanced on Tuesday when Kim Clijsters withdrew from their match because of a shoulder injury.