MELBOURNE, Australia -- No.7 seed Coco Gauff opened her 2023 Australian Open campaign with a straight-sets win over the Czech Republic's Katerina Siniakova. The 18-year-old American advanced to the second round with a 6-1, 6-4 win. 

Gauff will face 2021 US Open champion Emma Raducanu next. 

Media Day: Gauff ready to go one step further at Melbourne Park

Along with No.3 seed Jessica Pegula's 6-0, 6-1 opening win over Jaqueline Cristian, and a three-set win for last year's finalist Danielle Collins, it was a confident start for the top-seeded Americans. 

Confident Pegula on hitting with Tiafoe and staying in the zone

Playing in her fourth Australian Open, Gauff opened up play on Rod Laver Arena and powered through the first set in just 22 minutes. Siniakova struck back in the second set and looked primed to take the match to a third set after winning the longest rally of the match -- 22 strokes -- and breaking Gauff to lead 4-2. 

The lead was short-lived. Gauff broke back immediately and once again to earn a chance to serve out the win. In the longest game of the match, Siniakova gamely saved six match points before the American closed out the win with a backhand volley winner. 

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"Really pleased with myself," Gauff said. "Katerina is a fighter I knew she was going to fight until the last point and she proved that today. I'm glad I stayed mentally right there."

Gauff finished the match with 24 winners to 18 unforced errors and won over 70% of her service points on the day. 

Collins battles through injury to beat Kalinskaya

No.13 seed Danielle Collins needed over three hours to hold off Anna Kalinskaya, winning 7-5, 5-7, 6-4. Despite battling an issue in her left knee, Collins struck 55 winners to Kalinskaya's 30 to win after 3 hours and 3 minutes. 

Collins finding a new recipe for success ahead of Melbourne return

Kostyuk knocks out Anisimova

Ukraine's Marta Kostyuk tapped into her successful history at Melbourne Park to oust No.28 seed Amanda Anisimova, 6-3, 6-4. Ranked No.61, the 20-year-old tallied the first upset of the tournament in 78 minutes, breaking Anisimova on each of the four break points she faced. Kostyuk proved the better aggressor in the match, hitting 29 winners to 16 unforced errors to Anisimova's 21 winners and 18 unforced errors. 

Kostyuk will face Australian wild card Olivia Gadecki in the second round. The 20-year-old Gadecki earned a win in Grand Slam debut, defeating Polina Kudermetova 7-5, 6-1.

Fruhvirtova, Lys, Gadecki lead AO 2023's Grand Slam debuts