Rafael Nadal came through his first hard-court match in nearly a year with a straight-sets win over Ryan Harrison at Indian Wells.
Nadal, who returned from seven months out with a knee injury last month, eased to a 7-6 (7-3) 6-2 victory.
Fourth seed David Ferrer became the first major casualty at the BNP Paribas Open, losing 3-6 6-4 6-3 to South African Kevin Anderson.
Second seed Roger Federer and women's top seed Victoria Azarenka both won.
Federer, who won his fourth Indian Wells title last year, lost just four service points in the first set on the way to his comprehensive 6-2 6-3 win over Russian Denis Istomin, and will next face Croatian Ivan Dodig.
Two-time Indian Wells winner Nadal, who had a bye in the first round as one of the top seeds, has won two out of three tournaments on clay since his comeback in February but admitted he was unsure how his knee would hold up on the hard surface.
The Spaniard, seeded fifth, lost three consecutive games to squander a 4-1 lead in the opening set against unseeded American Harrison, but he won the tie-break and took the second set with ease. He will face Leonardo Mayer in the third round.
The 26-year-old said: "My physical performance needs to improve. My movements need to improve.
"After seven months out I don't want to take crazy risks but when I am playing in a tournament my mentality is to try my best in every moment. I am satisfied to be in the next round. That's the most important thing.
"The victory is important because it gives me the chance to play another day and I need to play matches and compete. Two weeks ago I didn't really know if I would be here playing. I am happy to be here.
"It was a good victory against a good opponent."
Ferrer, who recently overtook fellow Spaniard Nadal to go fourth in the rankings, had a bye in the first round but went down 3-6 6-4 6-3 to the unseeded South African in round two.
Anderson will face Jarkko Nieminen in round three after the Finn thrashed 29th seed Fernando Verdasco 6-1 6-0.
Australian Lleyton Hewitt pulled off a shock when he beat last year's runner-up John Isner 6-7 (6-8) 6-3 6-4, while Latvian Ernests Gulbis extended his winning streak to 12 matches with a 6-2 6-0 demolition of ninth seed Janko Tipsarevic.
In the women's draw, defending champion Azarenka won through to the third round with a 6-4 6-1 victory over Slovakian Daniela Hantuchova, while fourth seed Angelique Kerber beat Irina-Camelia Begu - - 6-3 6-2.
"I have to give her credit, I think she started really well," said Azarenka. "It caught me a little bit off-guard.
"I needed a little bit of time to realise that I'm in the tournament, that I have to step it up if I want to win the match."
Seventh seed and former US Open champion Samantha Stosur was an early winner as she beat American Madison Keys 6-3 6-4, and eighth seed Caroline Wozniacki battled past Alize Cornet 6-4 3-6 6-3.
Andy Murray warmed up for his second-round match against Russia's Evgeny Donskoy by teaming up with brother Jamie in the men's doubles.
The Scottish pair enjoyed a 6-4 4-6 10-4 victory over Sweden's Robert Lindstedt and Serbia's Nenad Zimonjic, the fifth seeds.