The 36th-ranked Azarenka, the 2009 and 2011 winner from Belarus, is playing in Miami for the first time since 2012. She missed the 2013 tournament with a right ankle injury and sat out last year with a left foot injury.

"It's been unfortunate the last couple of years for me, but I love this tournament," said Azarenka, a two-time Australian Open champion. "I'm just looking forward to build my momentum here again and try to play as many matches as possible."

The left foot injury plagued Azarenka throughout last season, limiting her to nine tournaments. This year, she reached the Doha final in February.

Azarenka took a 4-1 lead in the first set before Soler-Espinosa held serve in the fifth game. In the second set, Azarenka initially trailed 3-1 before winning the next five games to end the match.

"I think it was a pretty good first set," Azarenka said. "Second set, there were a bit too many mistakes in the beginning."

American Jack Sock, also making a comeback after having surgery in December to repair a right pelvic muscle, advanced with a 6-3, 6-4 victory over Go Soeda of Japan.

The 45th-ranked Sock also spent three weeks in February bedside at a hospital with 24-year-old brother Eric, who was near death suffering from Lemierre's Syndrome.

"The biggest thing for me, in the back of the mind, to go out and play a pretty physical game," Sock said. "To be able to go out and know that I can play every point the way I need to."

Two American women also advanced to the second round.

Christina McHale beat Romanian wild-card Sorana Cirstea 7-5, 6-4, and Alison Riske topped Mirjana Lucic-Baroni of Croatia 6-4, 6-0. (***)

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