Dinara Safina saw off another shaky match and then saw her path to the final open up with the upsets of Elena Dementieva and Jelena Jankovic.

World number one Safina, with a debate raging about her worthiness to hold the highest ranking in the women's game without a grand slam title to her name, reached the third round at Flushing Meadows with a win over Germany's Kristina Barrois.

Safina had been less than impressive in her first-round win over wild card Olivia Rogowska, coming from 0-3 down in the final set to beat the Australian, and against the world number 67 from Germany she had a similarly frustrating experience.

The Russian took two hours and 13 minutes to eke out at 6-7 (7-5), 6-2, 6-3 victory, giving up 15 double faults and committing 38 unforced errors to 36 winners.

"Another tough day in the office," Safina said afterwards. "Another day off tomorrow and another match on Saturday.

"Actually today I think I was serving in some stages better than the first round. That's a positive and at least I made some aces.

"Previous round I didn't make any ace and made only double faults. It's better, still not perfect but I know what the problem is.

"There is no problem in the technique, just in my head, so I have to change the chip in here," she added pointing to her head.

Having fought so hard to make a match of it, Barrios ironically gave up the contest with a double fault but Safina said she was looking for a vast improvement and a short day's work in the third round, when she will face Czech player Petra Kvitova, ranked 72 in the world.

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Fourth seed Dementieva became the first big-name casualty of the 2009 US Open when American teenager Melanie Oudin claimed another big-name grand slam scalp.

Oudin, 18 later this month, had caused a shock at Wimbledon earlier this summer when she knocked out Jankovic in the third round and the world number 70 added the 2008 Olympic champion to her list of victims at Arthur Ashe Stadium with a 5-7, 6-4, 6-3 upset victory.

Having allowed Oudin to level the match at 1-1, Olympic champion Dementieva quickly allowed the American to take the initiative in the final set and not even a medical timeout for treatment on an injured left thigh could stop the underdog from having her day.

Serving for the match the American quickly gave herself triple match point. The fourth seed saved the first two in clinical fashion but then Oudin sent down a big serve wide to the Russian's backhand and the netted return sparked loud celebrations as the American booked her ticket to the third round and a possible meeting with No.29 and former champion Maria Sharapova, who was set to play American wild card Christina McHale in a night session match.

Dementieva was gracious in defeat.

"For sure it is disappointing, I was really hoping to play well here but just didn't feel the way I should .

"Maybe overplayed a bit in the summer but I think she played really well. She was very positive and going for the shots, going for the winners. Just was a very solid game from her."

While Dementieva was removed from the picture as Safina's seeded opponent for the semi-finals, Jankovic had been the expected threat in the quarter-finals for the top seed.

The fifth seed, though, fell foul of Kazakhstan's Yaroslava Shvedova, losing a final-set tie-break to the world number 55, 6-3, 6-7 (4-7), 7-6 (8-6).

Shvedova will now meet world number 40 Gisela Dulko of Argentina in the fourth round after she knocked out 30th seed Alona Bondarenko, brushing aside the Ukrainian 6-4, 6-0.

There are now no other seeds left in Safina's quarter of the draw after Austria's Patty Schnyder, the number 19, was ousted by Italy's Sara Errani, 7-5, 6-2, and 23rd seed Sabine Lisicki was beaten by Australian qualifier Anastasia Rodionova, the world number 139 who knocked Britain's Elena Baltacha out in the final qualifying round.

There was further trouble for Lisicki when she fell during the deciding point and needed extensive treatment on her left ankle as she lay in tears on the court.

There was considerably less drama for sixth seed Svetlana Kuznetsova, the 2004 champion and this year's French Open winner. The Russian knocked out Latvia's Anastasija Sevatova 6-4, 6-2.

Ninth seed Caroline Wozniacki of Denmark, who beat Croatian Petra Maric 6-1, 6-0 to set up a third meeting with Romanian 24th seed Sorana Cirstea, who was taken to three sets by Stephanie Dubois of Canada before winning 6-4, 5-7, 6-4.

Nadia Petrova, the 13th seed from Russia, overcame stubborn resistance from Frenchwoman Julie Coin before coming out a 6-4, 7-6 (7-3) winner. Petrova will next face Jie Zheng of China, the No.21, who beat Alize Cornet of France 1-6, 6-3, 6-3.