In her first match since winning the Australian Open, women's world number two Naomi Osaka beat Ajla Tomljanovic 7-6 (7/3), 6-4.
Daniil Medvedev has celebrated his rise to second in the world with a seamless entry into the Miami Open, trouncing Taiwan's Lu Yen-Hsun in less than an hour.
Russia's Medvedev needed just 56 minutes to subdue Lu 6-2, 6-2, firing nine aces with just one double fault as he advanced to a third-round meeting with Australian Alexei Popyrin, a 6-4, 6-2, winner over 30th-seeded American Reilly Opelka.
Women's world number two Naomi Osaka, seeded second behind top-ranked Australian Ashleigh Barty, had a tougher time, but conquered her nerves in her first match since winning the Australian Open to beat Aussie Ajla Tomljanovic 7-6 (7/3), 6-4.
Men's third seed Alexander Zverev, ranked seventh in the world, became the biggest upset victim so far in the prestigious ATP Masters and WTA hardcourt tournament, falling 1-6, 6-3, 6-1 to 83rd-ranked Finn Emil Ruusuvuori.
Medvedev, the top seed in an ATP Masters event for the first time, was all over Lu from the opening game.
He belted 24 winners to become the second player – along with compatriot Andrey Rublev – to reach 15 match wins this year.
Runner-up to top-ranked Novak Djokovic at the Australian Open, Medvedev ascended to No. 2 in the world when he lifted the ATP trophy in Marseille.
Medvedev became the first player outside the "Big Four" of Djokovic, Roger Federer, Rafael Nadal and Andy Murray to rank second in the world since Lleyton Hewitt in 2005.
But he's already looking for more.
"The only thing I feel like when you reach something you haven't done then straight away it doesn't matter and you want to go further and further," he said. "I think it's the same for everybody.
"I'm happy about my achievement but only trying to improve every day and want to go further."
Zverev also arrived in Miami riding a wave of success, having captured the ATP title in Acapulco last week.
But Ruusuvuori, 21, rallied to claim one of the biggest wins of his career, turning the tables on Zverev with more aggressive tactics in the second set and posting the second win of his career over a top-10 player.
"I don't even know myself," he said of how he managed the reversal. "I wasn't feeling very comfortable in the first set and I was making a lot of unforced errors. But slowly in the second I was starting to feel a bit better."
Osaka fights through
Osaka acknowledged she was feeling some nerves in her first match since she lifted her fourth Grand Slam title in Melbourne.
"I would say what I'm most proud of today, just being able to handle my nerves," she said.
That was a bigger problem than the gusty wind on Grandstand Court at Hard Rock Stadium, where 77th-ranked Tomljanovic twice went up a break in the opening set but despite an impressive display of power was eventually undone by 24 unforced errors.
Thirteen aces among her 36 winners helped Osaka overcome a slew of unforced errors of her own and set up a third-round meeting with Serbian qualifier Nina Stojanovic, who surprised Yulia Putintseva, the 26th seed from Kazakhstan, 5-7, 7-5, 6-2.
"I served really well when I needed to," Osaka said. "Unfortunately I got broken a couple of times, but I think when it really, really mattered, I was able to serve well, so I'm happy with that.
Fourth-seeded American Sofia Kenin, the 2020 Australian Open champion, rallied for a 6-7 (6/8), 6-1, 6-3 victory over German Andrea Petkovic.
Sixth-seeded Karolina Pliskova, eighth-seeded Bianca Andreescu and No. 12 Garbine Muguruza also advanced.
Pliskova beat China's Zheng Saisai 6-2, 6-1, Andreescu defeated Czech Tereza Martincova 7-6 (7/5), 6-2 and Spain's Muguruza, coming off a title in Dubai two weeks ago, beat wild card Wang Xinyu of China 6-4, 6-1.
In other men's action, Australian James Duckworth surprised eighth-seeded Belgian David Goffin 6-3, 6-1 and Britain's Cameron Norrie beat ninth-seeded Bulgarian Grigor Dimitrov 7-5, 7-5.