Six months after lifting the Wimbledon trophy, world number seven Vondrousova became the highest seed to fall so far in round one of the opening major of the year.
The Czech, who pulled out of a warm-up event with a hip injury, was beaten 6-1 6-2 by Ukrainian qualifier Dayana Yastremska.
Yastremska said afterwards that her grandmother’s house was recently hit by a rocket in the ongoing war in her home country.
The 23-year-old said the resistance showed by her country against the Russian invasion is what motivates her on court.
“To talk about what is going on in Ukraine in a couple of seconds is not enough,” she said in her on-court interview.
“I’m proud of Ukraine, proud of the people, the warriors and the people.
“When I was in Brisbane, before the match I was told a rocket arrived on my grandmother’s house. It was hard to play.
“We need to remember about [the war] and give as much support to Ukraine as possible.”
Elina Svitolina, another Ukrainian who has spoken at length about the impact of the war, is also through.
The 19th seed needed 59 minutes to complete a 6-2 6-2 win over Australian wildcard Taylah Preston.
Tunisian sixth seed Ons Jabeur took just 67 minutes to beat Ukrainian qualifier Yuliia Starodubtseva 6-3 6-1. The two-time Wimbledon runner-up will face 16-year-old Mirra Andreeva next after the Russian beat American Bernarda Pera 7-5 6-2.
But Croatian 21st seed Donna Vekic lost 6-4 6-4 to Russian Anastasia Pavlyuchenkova, while Czech 31st seed Marie Bouzkova had an early exit against 19-year-old compatriot Linda Noskova, losing 6-1 7-5.
Spain’s former world number two Paula Badosa, who missed the second part of 2023 with a stress fracture in her back, returned to Grand Slam tennis with a 6-1 6-3 win over American Taylor Townsend and will face 2021 French Open runner-up Pavlyuchenkova next.