New York - Former Wimbledon champion Petra Kvitova and 2009 US Open runner-up Caroline Wozniacki withstood challenges from tenacious Asian rivals to reach the second round of the US Open on Tuesday.
With world number one Novak Djokovic waiting for a night opener and 17-time Grand Slam champion Roger Federer having his start pushed back by rain, women took center stage in the early going at Arthur Ashe Stadium.
Czech seventh seed Kvitova, the 2011 Wimbledon winner, fought off Japan's 92nd-ranked Misaki Doi 6-2, 3-6, 6-1 while Danish sixth seed Wozniacki dispatched 133rd-ranked Chinese qualifier Duan Ying-Ying 6-2, 7-5.
World number one Djokovic, a six-time Grand Slam champion who captured his fourth Australian Open crown earlier this year, launches his quest for a fourth consecutive US Open final when he faces Lithuanian Ricardas Berankis.
Seventh-seeded Swiss star Federer, at his lowest spot in the US Open order since 2002, will face Slovenia's Grega Zemlja in a match postponed from Monday due to rain.
"I was ready to play last night, I enjoy the night sessions, but it's a quick turnaround," Federer said.
"I have played Grega only twice so you can't really take too much from that. We know each other's strengths and weaknesses."
Duan made 46 unforced errors but kept pressure on Wozniacki, who battled to avoid a repeat of last year's US Open first round ouster while boyfriend Rory McIlroy, a two-time major golf champion, watched from the stands.
"She just went out and hit on every shot," Wozniacki said.
"If she was in the court or not, it was going 100 mph. I had to keep going.
"I had to fight for every point. She couldn't keep up that level forever."
Duan broke Wozniacki in the second game of the second set and exchanged breaks on the way to a 5-2 lead, but Wozniacki broke in the ninth game, fought off a set point in the 10th to pull even at 5-5, then broke again in the 11th.
Serving for the match, Wozniacki was pushed to break point twice, saving the first with a forehand winner and the last when Duan hit a backhand long, then won after one hour and 41 minutes when Duan netted a forehand, booking a date with a South African foe, Chanel Simmonds or Chanelle Scheepers.
"She got a little tight at the end," Wozniacki said.
"And I got a bit lucky as well."
Doi, a 22-year-old left-hander whose only prior US Open appearance ended with a 2011 first-round cramping retirement, tested Kvitova in breezy conditions.
"The wind was quite difficult for us both," Kvitova said.
"In the first round of Grand Slams it's difficult all the time so you have to be focused.
"I didn't play my game all the match. I didn't have focus. I have to have more confidence."
The US Open is the only Grand Slam event where Kvitova, who booked a second-round match against Serb Bojana Jovanovski, has not reached the semi-finals, her best runs being to the fourth round in 2012 and 2009.
"I like Wimbledon, which is very calm," Kvitova said.
"Here it's more crowd and big show. I like matches on the big stadium too but the people are everywhere.
"It's too much crowd."
Kvitova is the highest-ranked rival in the quarter of the draw with Belarus second seed Victoria Azarenka, who begins her quest for a return to the US Open final later against German Dinah Pfizenmaier.
Azarenka, a two-time Australian Open winner, lost to world number one Serena Williams in last year's Flushing Meadows title match.
Serb 13th seed Ana Ivanovic, the 2008 French Open winner, beat Georgian Anna Tatishvili 6-2, 6-0 in 58 minutes. She faces Romanian Alexandra Dulgheru next.
Ivanovic reached the last eight at the US Open for the first time last year, her first Slam quarter-final since her Roland Garros title run.
Russian 14th seed Maria Kirilenko, the fiancee of National Hockey League Most Valuable Player Alex Ovechkin, ousted 2009 US Open semi-finalist Yanina Wickmayer of Belgium 6-1, 6-1.
The boyfriend of injury-sidelined Russian women's star Maria Sharapova, Bulgarian 25th seed Grigor Dimitrov, was eliminated by Portugal's Joao Sousa 3-6, 6-3, 6-4, 5-7, 6-2.
Canadian 10th seed Milos Raonic fired 28 aces in beating Italy's Thomas Fabbiano 6-3, 7-6 (8/6), 6-3, while US 13th seed John Isner blasted 16 aces to down Italy's Filippo Volandri 6-0, 6-2, 6-3.
Argentine qualifier Maximo Gonzalez upset 14th seed Jerzy Janowicz 6-4, 6-4, 6-2 as the Wimbledon semi-finalist from Poland struggled with back pain.
US Open results on Tuesday at Flushing Meadows (x denotes seeded player):
Jarkko Nieminen (FIN) bt Lukasz Kubot (POL) 7-5, 7-5, 6-2
Joao Sousa (POR) bt Grigor Dimitrov (BUL x25) 3-6, 6-3, 6-4, 5-7, 6-2
Julien Benneteau (FRA x31) bt Michal Przysiezny (POL) 6-4, 5-7, 6-4, 6-4
Pablo Andujar (ESP) bt Thiemo de Bakker (NED) 6-4, 6-4, 6-4
Milos Raonic (CAN x10) bt Thomas Fabbiano (ITA) 6-3, 7-6 (8/6), 6-3
Maximo Gonzalez (ARG) bt Jerzy Janowicz (POL x14) 6-4, 6-4, 6-2
Adrian Mannarino (FRA) bt Horacio Zeballos (ARG) 4-6, 6-4, 6-2, 6-1
John Isner (USA x13) bt Filippo Volandri (ITA) 6-0, 6-2, 6-3
Gael Monfils (FRA) bt Adrian Ungur (ROM) 6-1, 6-2, 6-0
Edouard Roger-Vasselin (FRA) bt Albert Montanes (ESP) 6-3, 6-2, 6-4
Philipp Kohlschreiber (GER x22) bt Collin Altamirano (USA) 6-1, 6-3, 6-1
Caroline Wozniacki (DEN x6) bt Ying-Ying Duan (CHN) 6-2, 7-5
Camila Giorgi (ITA) bt Jana Cepelova (SVK) 6-2, 6-2
Su-Wei Hsieh (TPE) bt Klara Zakopalova (CZE x31) 6-3, 6-3
Elena Vesnina (RUS x22) bt Annika Beck (GER) 6-1, 6-1
Karin Knapp (ITA) bt Grace Min (USA) 6-3, 6-1
Lucie Safarova (CZE) bt Lesya Tsurenko (UKR) 6-3, 2-6, 6-4
Roberta Vinci (ITA x10) bt Timea Babos (HUN) 6-4, 6-2
Maria Kirilenko (RUS x14) bt Yanina Wickmayer (BEL) 6-1, 6-1
Michelle Larcher de Brito (POR) bt Eleni Daniilidou (GRE) 6-4, 6-3
Flavia Pennetta (ITA) bt Nicole Gibbs (USA) 6-0, 6-2
Petra Kvitova (CZE x7) bt Misaki Doi (JPN) 6-2, 3-6, 6-1
Bojana Jovanovski (SRB) bt Andrea Petkovic (GER) 6-2, 6-4
Julia Glushko (ISR) bt Nadia Petrova (RUS x20) 6-3, 6-4
Ana Ivanovic (SRB x13) bt Anna Tatishvili (GEO) 6-2, 6-0
Alexandra Dulgheru (ROM) bt Varvara Lepchenko (USA) 6-7 (5/7), 6-2, 7-6 (7/5)
Christina McHale (USA) bt Julia Gorges (GER) 6-4, 6-3
Alize Cornet (FRA x26) bt Maria Joao Koehler (POR) 6-3, 6-2
Ajla Tomljanovic (CRO) bt Casey Dellacqua (AUS) 3-6, 6-1, 6-4