NEW YORK: Second seed Simona Halep survived a scare at the U.S. Open by overtaking American wild card Danielle Collins 6-7 (2), 6-1, 6-2 in Monday's opening center court match.

The French Open finalist moves on to face Slovakian Jana Cepelova, a 2-6, 7-5, 6-1 winner over Spain's Maria-Teresa Torro-Flor, in the second round of the season's last grand slam.

But the 22-year-old Romanian had a tricky time getting by Collins, a U.S. college champion from the University of Virginia.

Down a break at 3-4, the 20-year-old American brought the set back on serve at 4-all and with her confidence growing the collegian ran away with the decider by taking advantage of a slew of errors from Halep.

That shock seemed to snap the Romanian back to attention, and bring her groundstrokes under control as she roared to victory over Collins, who was playing her first tour-level main draw match.

"She played a tough match, I want to congratulate her," world number two Halep said in an on-court interview. "First set I was a little bit nervous. This court is huge.

"It's my best ranking ever and best moment of my life. I have to enjoy it, but it's not easy. Everybody is telling me I have chances to win this title."

Halep, who broke through last season by notching her first six career tour titles, has two titles this season and finished runner-up to Maria Sharapova at Roland Garros in her first grand slam final.

Polish fourth seed Agnieszka Radwanska took just 47 minutes to hand out a 6-1, 6-0 US Open first round rout to Canada's Sharon Fichman on Monday.

Radwanska allowed her 112th-ranked opponent just three points in the second set.

The 25-year-old Pole, who has never got beyond the fourth round in New York, goes on to face either Peng Shuai or Zheng Jie, who face-off in an all Chinese duel, for a place in the third round.

Later Monday night, Wimbledon champion Novak Djokovic switches his focus from family life to launch his bid for an eighth Grand Slam singles title at the US Open.

The world No. 1 from Serbia and women's French Open champion Maria Sharapova are the star attractions on the opening day of the year's last Grand Slam -- set to shine under the lights on Arthur Ashe Stadium court.

With two-time defending women's champion Serena Williams and five-time men's champion Roger Federer waiting in the wings, Monday's slate featured two other former champions in Andy Murray and Venus Williams, along with 2014 Australian Open winner Stan Wawrinka and women's world number two Simona Halep.

World No. 1 Djokovic, recently married and soon to be a father for the first time, is gunning for a fifth straight US Open finals appearance and a second title to add to the one he won in 2011.

He was set for a first career meeting with Diego Schwartzman, a 22-year-old from Argentina who is playing in his second career Grand Slam and the first tour-level hardcourt tournament of his career.

"I know he's very quick on the court," Djokovic said. "He's had his best results on clay. It's obviously always tricky to play against somebody I never faced before. And playing on the center court for Schwartzman will be a unique experience.

"He definitely has nothing to lose. I'm going to try to use my experience playing many matches on the center court and get a win."

Sharapova, who won her fifth career Grand Slam title at Roland Garros this year, returns to Flushing Meadows after missing last year's US Open with a shoulder injury.