Coco Gauff, Jessica Pegula into Australian Open's 2nd round

Coco Gauff advances to the 2nd round of the Australian Open (0:35)

Coco Gauff defeats opponent Katerina Siniakova on her seventh match point. (0:35)

MELBOURNE, Australia -- Americans Jessica Pegula, Coco Gauff and Danielle Collins reached the second round in contrasting fashion at the Australian Open on Monday.

Third-seeded Pegula overwhelmed Jaqueline Cristian of Romania 6-0, 6-1, while seventh-seeded Gauff overcame a second-set wobble to beat Katerina Siniakova 6-1, 6-4.

Collins, the runner-up last year to Ash Barty and seeded 13th, battled a left knee injury while defeating Anna Kalinskaya 7-5, 5-7, 6-4.

Pegula and Gauff could meet in the semifinals, while Collins could play No. 1 Iga Swiatek in the fourth round.

A quarterfinalist in Melbourne in each of the past two years, Pegula needed just 59 minutes to get past the 161st-ranked Cristian, who was appearing in her third Grand Slam event.

"Today is just one of those days everything was working," said the American, who will play either Czech qualifier Brenda Fruhvirtova or Aliaksandra Sasnovich in the second round.

"Always feels good when you win a match like that. I think when those days come, you just kind of take it and don't complain and don't critique. You kind of just move on to the next one."

Gauff, who reached her first Grand Slam singles final at the French Open last year, was given the honor of opening proceedings on Rod Laver Arena and dominated Siniakova in the first set.

The Czech player led 4-2 in the second set, but Gauff rallied and clinched victory on her seventh match point.

"I was not expecting to open the tournament on Rod Laver," Gauff said. "I'm super-honored that the tournament chose me and Katerina. I'm really pleased with myself. Katerina's a fighter. I knew she was going to fight for every point. I just stayed strong mentally."

Gauff will now play former US Open champion Emma Raducanu after the British player shrugged off a bothersome left ankle issue to beat Tamara Korpatsch of Germany 6-3, 6-2.

Collins required a medical timeout for a left knee issue early in the first set of her match with Kalinskaya but survived to win in just over three hours.

Another former US Open champion, Bianca Andreescu, advanced to the second round, but 28th-seeded Amanda Anisimova was beaten 6-3, 6-4 by Marta Kostyuk.