Ostapenko and Garcia progress in Adelaide but Vondrousova out injured
Czech world number seven Vondrousova began her season at the United Cup, beating Serbia's Olga Danilovic and losing to China's Zheng Qinwen.
She was seeded three in Adelaide and due to play her first-round match on Tuesday evening. But the WTA said she had withdrawn, citing a hip injury. It was not clear how serious the problem was.
Former French Open winner Ostapenko, the Latvian sixth seed and world number 12, needed three sets to get past Romanian opponent Sorana Cirstea 2-6, 6-2, 6-4.
She lost serve twice in the first set before waking up.
"I was sleeping in the first set, I'm not really a morning person," she said after an morning start at Memorial Drive
"It took me time to wake up and get into the match. I'm glad I managed to win it."
Ostapenko recovered to win six games out of seven and reach 3-1 in the final set.
"I like to play in Australia," the 2023 Australian Open quarter-finalist said.
"Conditions are good for me. Sometimes I get too worked up but then I calm down and play better."
She will next play former world number four Garcia, now ranked 20th, who also avoided an upset, coming from a break down in the final set to defeat Australian wildcard Taylah Preston 6-4, 1-6, 6-3.
Germany's Laura Siegemund, part of the country's winning United Cup team, dismissed seventh seed Liudmila Samsonova 6-7 (1/7), 6-4, 6-4.
Eighth seed Veronika Kudermetova also progressed, but former world number one Karolina Pliskova lost 6-2, 6-1 to qualifier Katerina Siniakova in an all-Czech match-up.
In men's action, a trio of Australians advanced, with Jordan Thompson, Chris O'Connell and Alex Bolt all posting straight-set wins.
At the WTA Hobart International, 2020 Australian Open champion Sofia Kenin swept past Belgium's Greet Minnen 6-3, 6-3.
But former US Open winner Sloane Stephens crashed out at the first hurdle to China's Yuan Yue 6-4, 3-6, 7-6 (7/5).
