NEW YORK (AFP) - Qualifier Julie Coin scored one of the biggest upset in US Open women's open era history Thursday, sending world No. 1 and top seed Ana Ivanovic crashing out in the second round.

Coin, who is ranked 188th in the world, was making her Grand Slam debut after successfully coming through the qualifying round. She had tried but failed earlier this year to qualify for the other three Grand Slams -- Australian Open, French Open and Wimbledon.

The 25-year-old Coin clinched the victory on her third match point in the one hour, 57 minute match at the main Arthur Ashe Stadium.

"Today I felt nervous at the beginning and then it went away," said Coin, of France. "I don't know how I did it.

"I am not thinking about anything right now. Just enjoying the moment."

Ivanovic looked the more nervous of the two in the deciding third set. She posted a total of eight double faults and made 37 unforced errors to 26 for Coin.

"This is very disappointing to me but something I have to accept," Ivanovic said. "I never saw her (Coin) play before so I didn't know what to expect.

"She played a lot better than I expected. She served very well."

Ivanovic, of Serbia, converted just one of her eight break-point chances and didn't record an ace.

She managed to survive two match points before going down in one of the biggest upsets in women's tennis history.

"I kept thinking play your game and get your first serve in," Coin said.

Until Coin's win, the top seed at the US Open in the open era had not lost earlier than the third round when Billie Jean King was ousted in the 1973 tournament.

Coin moves through to the next round where she will play French countrywoman Amelie Mauresmo.

"It will be like playing a No. 1 because she used to be No. 1," Coin said of Mauresmo.

Coin, who broke Ivanovic's serve five times, double faulted on her first match point. Her second match point came two points later and it took a superb crosscourt forehand directly on the line for Ivanovic to stay in the game.

Coin clinched the win when Ivanovic sailed a forward wide and long on the third match point.

Ivanovic has not had a long reign at number one. Her stay at the top was interrupted for a week earlier this month, but she since regained the top spot in the WTA rankings.

Ivanovic came into the final Grand Slam of the year complaining about a lack of preparation due to injuries.

A muscle strain in her leg did not allow her to play any tuneups prior to Wimbledon, where she made another disappointing exit in the third round.

Later she suffered a right thumb injury, which played a part in her second-round loss last month at the Rogers Cup in Montreal, Canada.

Swelling in the hand forced her to withdraw from the Beijing Olympics where she was the top seed.

In between Beijing and New York she flew to Australia to get more treatment on the hand.

But she wasn't making excuses on Thursday.

"Today I didn't feel it," she said of the thumb. "I'm just happy to be back on track without pain.

"Now all I have to do is put some hard yards on the court and go back out there and work hard."

Sixth seed Dinara Safina advanced to the third round by beating Roberta Vinci of Italy 6-4, 6-3 in a second round match.

It has been a breakthrough season for Safina who has won three of her eight career titles in 2008. She reached the final at the Beijing Olympics but had to settle for silver after losing to Russian compatriot Elena Dementieva.

Safina hammered six aces and won 71 percent of her first serve points in the 80-minute match on the main Arthur Ashe Stadium.

"I think it still could be better," she said. "There is more room to improve. Hopefully in the next match I can do better."

It would be a windfall victory for Safina if she breaks through and captures the US Open title.

She placed first the US Open Series leading up to the final Grand Slam of the season which means she will receive a one million dollar bonus in addition to the 1.5 million dollars in first place prize money.

Safina, of Russia, moves through to the third round where she will play Timea Bacsinszky of Switzerland.

In another women's match Thursday, two-time champion Venus Williams defeated Rossana De Los Rios 6-0, 6-3.

The seventh-seeded Williams moves through to the third round where she will play Alona Bondarenko who beat Sabine Lisicki 6-4, 1-6, 6-4 on Thursday.

Japan's Kei Nishikori advanced when Roko Karanusic, of Croatia, retired at the end of the second set with the Japanese teen leading 6-1, 7-5.

Nishikori, who is playing in his first US Open, advances to the third round where he will face the winner of a match between fourth seed David Ferrer, of Spain, and Andreas Beck of Germany.

"I tried to go to the net more often, because he was using the slice a lot," Nishikori said. "I tried to make more first serves. He gets more nervous when I make my first serve."