Former US Open champion Sloane Stephens battled into the second round of the season-opening Brisbane International with a hard-fought 7-5, 6-3 win over Katerina Siniakova on Sunday.
Stephens, who reached a career-best ranking of three in 2018, broke her Czech opponent once in each set to book a second-round clash against 13th seeded Belgian Elise Mertens.
"It was obviously a good match," Stephens said.
"It's always really tough starting the year – you just don't really know what's going to happen, so I think being able to come here and get a win was really nice.
"I'm really proud of that performance."
In other first-round matches, there were wins for Ukraine's Marta Kostyuk over Romanian Ana Bogdan 4-6, 6-3, 6-3, and Italian Camila Giorgi, who beat American Peyton Stearns 5-7, 6-2, 6-3.
Australian wildcard Arina Rodionova upset higher-ranked Italian Martina Trevisan 6-3, 6-2, while Anna Kalinskaya downed American Bernarda Pera 6-2, 6-1.
Russian teenager Mirra Andreeva beat countrywoman Diana Shnaider 6-2, 6-3.
Former world No 1 Naomi Osaka begins her comeback on Monday when she plays Germany's Tamara Korpatsch.