NEW YORK (AP) — This U.S. Open finally got its first shockers.

After three days of the top players not only winning but winning decisively, the biggest news Thursday came off the court, with Andy Roddick announcing his impending retirement.

On the court, fifth-seeded Jo-Wilfried Tsonga was upset by Martin Klizan of Slovakia in the second round. The 52nd-ranked Klizan won 6-4, 1-6, 6-1, 6-3.

Before Tsonga's loss, top-five seeds on the men's and women's sides had played 14 matches — and won all 14 in straight sets.

Roddick called a news conference Thursday evening to say that he'll call it a career after his last match at this tournament, which he won in 2003.

"I don't know that I'm healthy enough or committed enough to go another year," he said on his 30th birthday, a day before facing Bernard Tomic in the second round. "I've always wanted to, in a perfect world, finish at this event."

Tsonga was the runner-up at the 2008 Australian Open and a semifinalist at Wimbledon this year. He had reached at least the third round in 18 straight Grand Slam trips.

"Today I was not in a good shape," he said. "I didn't play good tennis. It seemed like I couldn't hit the ball enough hard to put my opponent out of position. I don't really know why it was like this today, but sometimes it's happen with me."

The 23-year-old Klizan had failed to make it past the second round in three previous Grand Slam appearances. He had never defeated an opponent ranked better than No. 49.

"I had no pressure," Klizan said. "If I lose, then I lose. I lose with (a) good player. But I won and I'm very happy. It means for me more that I beat finally a guy from top 10."

This year's Open has generated plenty of drama in one area: comebacks from two sets down. American Mardy Fish rallied to beat Nikolay Davydenko 4-6, 6-7 (4), 6-2, 6-1, 6-2, the 10th time in this tournament a man had won after losing the first two sets — already an Open record.

The 30-year-old Fish, seeded 23rd, missed two months this season because of an accelerated heartbeat but showed few signs of fatigue in playing nearly 3 1/2 hours.

And after Tsonga lost, another top-five seed was at least pushed beyond a straight-sets finish. Second-seeded Agnieszka Radwanska was down a set and a break to 39th-ranked Carla Suarez Navarro. Then she won 11 straight games for a 4-6, 6-3, 6-0 victory.

Serena Williams beat old nemesis Maria Jose Martinez Sanchez 6-2, 6-4. Seeded fourth, Williams overcame six double-faults and 24 unforced errors — she had 32 winners to five for Martinez Sanchez.

In the 2009 French Open third round, Williams hit a ball she was sure went off Martinez Sanchez's arm, then said the Spaniard cheated by not acknowledging it.

Jack Sock also reached the third round at a major tournament for the first time. The 19-year-old from Nebraska beat Flavio Cipolla 6-2, 6-2, 6-4.

Sock, ranked 248th, got in with a wild card. He saved 12 of the 13 break points he faced, while converting all six he earned on the 88th-ranked Cipolla's serve.

Next up is a meeting with No. 11 Nicolas Almagro of Spain, a 6-3, 5-7, 5-7, 6-4, 6-4 winner over Philipp Petzschner.

Sixth-seeded Tomas Berdych and American Sam Querrey, seeded 27th, advanced with straight-set victories.

No. 1 Roger Federer opened the night session at Arthur Ashe Stadium against 83rd-ranked Bjorn Phau. Then sixth-seeded Angelique Kerber takes on seven-time Grand Slam champion Venus Williams, the juicy second-round match made possible because the American is unseeded after missing time because of illness.