Venus Williams, in only her second WTA match after a long illness layoff, upset world number three Petra Kvitova on Friday to reach the third round of the WTA and ATP Miami hardcourt tournament.
World number two Rafael Nadal cruised in his opener and women's top seed Victoria Azarenka stretched her win streak to 24 matches at the $9.6 million event, but seven-time Grand Slam singles champion Williams stole the show.
"It's definitely a big step forward," Williams said after her 6-4, 4-6, 6-0 win. "To win these matches definitely a lot of it is mental, to get out there and believe you're going to win and execute.
"How I'm going to do, I never really know, so it's great to have a win like this. It's definitely satisfying."
Williams withdrew from last year's US Open with the auto-immune disorder Sjogren's syndrome, an illness that saps energy and causes joint pain. Her first tournament match since then was a first-round triumph on Wednesday.
That put Williams up against Czech third seed Kvitova, who fought to reach a third set only to be overpowered by Williams after two hours and 18 minutes.
"I was just trying to win the match. I didn't even think about that it was six-love until like long after the match was over," Williams said.
Kvitova was impressed with how well Williams played after seven months away in booking a third-round match-up with Canadian wildcard Aleksandra Wozniak, who defeated Romania's Monica Niculescu 4-6, 6-3, 6-4.
"She played very well after a long time. She looks very ready, very fit," Kvitova said. "The third set was really cruel for me. I knew what I had to do, but if I don't return very well it's tough to play against her."
Williams said she was playing with new enthusiasm.
"I'm pretty pumped out there. Like literally I have nothing to lose," she said. "Every shot is a victory and a blessing so I'm just going for it. Hopefully I have a new lease on life. I just want to feel good enough to play."
Spanish second seed Nadal began his quest for a first-ever Miami title by ousting Colombia's Santiago Giraldo 6-2, 6-0 in 69 minutes, saying it was not as easy a victory as he made it seem.
"I played a very solid match with no mistakes," Nadal said. "No match is easy, even if the score was very easy because 6-2, 6-0 is a big difference in the score but not in the tennis. You have to fight every point. You have to find solutions every moment."
Nadal next has a third-round date with Czech Radek Stepanek, who ousted Germany's Tommy Haas 7-6 (7/4), 6-1.
Women's world number one Azarenka eliminated Dutch player Michaella Krajicek 6-3, 7-5. Azarenka broke as Krajicek served for the second set, then held and broke again to close out the match after one hour and 42 minutes.
Azarenka, from Belarus, stretched her season-long win streak to 24 matches. She has the best start to a WTA season since Martina Hingis won 37 in a row in 1997.
"I'm not really thinking about numbers or the streaks," Azarenka said. "My job is to play tennis. I just try to stay focused every day and try to be the best player I can."
Top seed Azarenka, who already has four titles this year, will next face British wildcard Heather Watson, who defeated Czech Lucie Safarova 6-2, 6-1. Azarenka has won both their prior meetings.
World number four Andy Murray eased into the third round by dispatching Colombia's Alejandro Falla 6-2, 6-3, avoiding a repeat of an embarrassing early ouster in Indian Wells.
Murray, 24, will next face big-serving Canadian 26th seed Milos Raonic, who advanced over France's Arnaud Clement 7-6 (9/7), 6-2.
Serbian world number one Novak Djokovic, winner of the past three Grand Slam men's singles tournaments, will start the defence of his title on Saturday against Marcos Baghdatis of Cyprus.
Russia's Alisa Kleybanova, a former top-20 player who has missed the past 10 months battling Hodgkin's lymphoma, was beaten in her second-round match by compatriot Maria Kirilenko 7-6 (7/1), 6-3.
"I can't say I'm disappointed," Kleybanova said. "This has been a good achievement for me."