Americans Jessica Pegula and Coco Gauff, the top seeds who were in action on Thursday, rolled to straight-set victories in the second round of the Miami Open.

Pegula, the third seed, blitzed qualifier Katherine Sebov of Canada 6-3, 6-1, and the sixth-seeded Gauff knocked off another Canadian, Rebecca Marino, 6-4, 6-3.

After her victory, Pegula said a little familiarity with her opponent, who is 172nd in the WTA rankings, helped.

"I luckily knew her a bit," said Pegula, who is ranked third in the world. "We were playing (International Tennis Federation events) around the same time, and she's been doing much better this year, starting to creep back up there and playing some good tennis."

Pegula dominated on her first-serve points, 69 percent to 52 percent, and even more so on her second serve, 78 percent to 33 percent.

Gauff built a 4-1 lead over Marino in the first set, but had her serve broken once as Marino tied the set at 4-4. Gauff held serve for a 5-4 lead, and then broke Marino for the second time in the set on her second set point.

Each player had her serve broken twice as the second set was tied 3-3, but Gauff won the final three games, including another break of Marino, to claim the match.

"Today it was an up-and-down match, honestly," Gauff said. "I did well in the returning part, considering (Marino is) a big server. I'm really happy with how I played.

"She's not an easy opponent. She makes a lot of big shots, doesn't really give you a lot of rhythm. You kind of just have to hang in there."

Unseeded Belgian Elise Mertens, who is ranked 39th in the world, defeated Daria Kasatkina of Russia 4-6, 6-2, 6-2. Kasatkina is the eighth seed and also eighth in the WTA ratings.

Other seeded players who won in straight sets included No. 12 Liudmila Samsonova of Russia, 14th-seeded Victoria Azarenka of Belarus, No. 20 Magda Linette of Poland, 24th-seeded Jelena Ostapenko of Latvia, No. 25 Martina Trevisan of Italy, 27th-seeded Anastasia Potapova of Russia, 29th-seeded Petra Martic of Croatia, and No. 30 Danielle Collins of the U.S.

Seeded players advancing in three sets included No. 10 Elena Rybakina of Kazakhstan, Paula Badosa of Spain, 13th-seeded Beatriz Haddad Maia of Brazil and No. 23 Qinwen Zheng of China.

Also, American Claire Liu defeated Julia Grabher of Austria in straight sets.

--Field Level Media