NEW YORK -- Polish teenager Agnieszka Radwanska produced a massive upset by beating defending champion Maria Sharapova 6-4 1-6 6-2 in the US Open third round on Saturday.
Radwanska was playing in only her sixth Grand Slam event.
Sharapova had been a red-hot favorite to coast into the last 16 playing in the first match up on the Arthur Ashe Stadium center-court.
The Russian glamour girl had won her opening two matches, both played at night, for the loss of just two games and had been on court only 101 minutes.
She started well by pushing the 18-year-old Pole onto the backfoot with her big groundstrokes and breaking her serve to lead 2-1.
But Radwanska, a top world junior last year, playing in just her sixth Grand Slam event, broke back immediately to level at 2-2.
In the blustery conditions Sharapova started to wobble on her serve and Radwanska broke again to lead 5-3.
Sharapova broke back immediately, but once again she struggled on her serve and a double fault gave the Pole set point which she converted with a crisp backhand down the line.
Radwanska took a 1-0 lead in the second set but Sharapova looked to have shrugged off the danger by reeling off eight games in a row to stand 2-0 up in the third.
But then another sloppy service game allowed Radwanska a way back.
The Pole leveled at 2-2 and then stunned Sharapova and the crowd by breaking again, helped by an 11th double fault from the Russian.
The defending champion was on the ropes and Radwanska provided the coup de grace by converting her fourth break point for a 5-2 lead thanks to a Sharapova forehand drive that died at the bottom of the net.
The Pole then served out confidently, a net cord going against Sharapova on match point.
"It wasn't nice losing eight games in a row, but I had nothing to lose by hitting every ball and I did it," Radwanska said.
"It was so windy and it was tough to serve," the Pole said. "I had problems too, but she made many mistakes and double faults and she looked a little bit nervous," Radwanska said. "It was a great feeling."
The 30th seed will play either Shahar Peer of Israel or Nicole Vaidisova of the Czech Republic for a place in the quarterfinals.
Sharapova gave her opponent credit for battling back after losing the eight successive games.
"A lot of girls in her position on a big stage in a big stadium against a top player sometimes get a little nervous," Sharapova said. "She held on there.
"You'd think I would have the momentum," Sharapova said, "but I just didn't really feel that way inside of me for some reason."
Sharapova became the first second-seeded woman to lose before the round of 16 at the Open since Andrea Jaeger in 1981. Her father could barely watch, moving from his front-row perch to a seat farther back during the final points.
"Definitely not an easy day in the office for me," said Sharapova.
"I could sit here all day long and come up with excuses and say how bad I played. But at the end of the day, my opponent won the match and I lost it.
"Better go on from here. Clearly it hasn't been my best year, but I have a whole future ahead of me. I'm not going to throw myself a pity party here."
Another 18-year-old provided a big shock when Hungary's Agnes Szavay ousted seventh seeded Russian Nadia Petrova 6-4 6-4.
She will next play Julia Vakulenko of Ukraine, a relative veteran at 24, who battled past another Russian Maria Kirilenko 6-2, 6-4.
Sixth seed Anna Chakvetadze scored a fourth straight win over India's Sania Mirza, 6-2 6-3 in 53 minutes.
Chakvetadze's next opponent will be either Swiss 11th seed Patty Schnyder or Austrian Tamira Paszek. E-mail to a friend