KEY BISCAYNE, Fla. >> Serena Williams punctuated points Saturday with theatrics worthy of a Grand Slam final. There were squeals, knee kicks, pirouettes and fist pumps, sometimes all at once.

In other words, Williams appeared to be 100 percent.

Showing no lingering effects from a recent knee injury, the seven-time Key Biscayne champion won her opening match at the Miami Open on Saturday, beating Monica Niculescu 6-3, 6-1.

The match was the first for Williams since she withdrew before the semifinals at Indian Wells last week, citing a right knee problem. She played without a wrap on her knee and said it’s feeling much better.

“It was a little sore in practice, but it was OK today,” she said.

Despite the lopsided score, the match was not without tension. Williams also beat Niculescu two weeks ago but nonetheless struggled at the start with the Romanian’s unorthodox game, which includes a squash-style slice forehand that creates lots of spin.

When flummoxed, Williams didn’t try to hide her emotions.

“I’m clearly frustrated,” she told the crowd afterward. “I just try not to explode, which is hard because I’m really passionate.”

The top-seeded Williams began to dominate when she started moving toward the net, and she won nine of the final 10 games. She’ll face 15-year-old American CiCi Bellis in the third round Sunday.

Serena’s sister Venus also advanced, beating Samantha Stosur 6-4, 7-6 (3). The older Williams’ opponent in the fourth round will be No. 4 Caroline Wozniacki, who rallied to beat Kaia Kanepi 4-6, 6-1, 6-3.

In men’s play, No. 11-seeded Jo-Wilfried Tsonga made a successful 2015 debut by beating American Tim Smyczek 6-4, 3-6, 6-3. Tsonga sat out the start of this year with a right arm injury.

“I didn’t expect to play my best tennis today,” Tsonga said. “But it’s normal when you didn’t play a couple of months. I hope it’s going to be better and better.”

American John Isner beat 17-year-old wild card Andrey Rublev of Russia, 6-3, 6-4. Rublev is the world’s No. 1-ranked junior.

“I needed to come out ready to play,” Isner said, “because he’s a very talented kid. Anything can happen.”

Another American, Jack Sock, eliminated No. 21 Fabio Fognini 7-6 (4), 6-1.

Eugenie Bouchard was upset in her opening match by qualifier Tatjana Maria 6-0, 7-6 (4). Bouchard, seeded No. 6, won less than half her service points, had five double-faults and was broken five times.

The Canadian, a Wimbledon finalist last year, is only 6-4 this year. Her career record at Key Biscayne fell to 1-3.

Maria, a German ranked 113th, beat a top 10 player for the first time since 2010.

“I’m going to take a day off,” Bouchard said, “and then I’m going to practice a lot and try to put this one behind me as soon as possible.”

Serena Williams had a first-round bye, and waited even longer to play because her opening match was postponed Friday night due to rain. She lives only 90 minutes from Key Biscayne, and took the court looking right at home in a pastel tangerine outfit and matching tennis bag.

She eased any doubts about her knee by chasing down a lob midway through the first set. On the run with her back to the net, she scooped back an improbable shot and went on to win the point.

“I was surprised I was able to get it,” she said. “I’m really fast when I want to be. I can get any ball I want to. My coach is always like, ‘If you want it, you can do it.’ I just have to want every ball. I guess I wanted to get to that.”

The two-time defending champion won her 13th consecutive match on Key Biscayne, and extended her winning streak on the tour this year to 16 matches.