It was just past 10:30 p.m. Tuesday when Serena Williams strode onto Arthur Ashe Stadium for her first-round match at the U.S. Open. And she was greeted like a rock star, showered with cheers, applause and ear-piercing whistles that could have hailed a New York City cab 10 blocks away.

It was a radically different vibe, in short, from Williams’s last singles match on Ashe, in 2009, when she trudged off amid controversy, having been defaulted from a semifinal against Kim Clijsters following a profane outburst at a lineswoman over a debatable foot-fault call.

Wearing a royal blue dress and cascading diamond earrings, Williams was a model of composure Tuesday, keeping tight rein on her emotions when she stepped onto the sport’s biggest stage for the first time in two years and even tighter control on her tennis strokes during the match.

The result was a 6-1, 6-1 evisceration of her woefully outmatched opponent, 19-year-old Bojana Jovanovski of Serbia, whom Williams dismissed in 56 minutes.

It was afterward, during her on-court interview with ESPN’s Pam Shriver, that Williams betrayed the slightest hint of emotion as she thanked those in the stands who stayed to the end.

“I’m so happy to be here,” said Williams, 29, who won her first U.S. Open in 1999, when her opponent Tuesday night was just 7. “I didn’t think I could make it.”

There were many reasons to wonder whether Williams would return to the sport at all following foot surgery in 2010 and a pulmonary embolism in February.

Williams not only returned in June, but she brought with her, in the months since, what women’s tennis had lacked in her absence: A player capable of matching her outsize power with a fierce competitive will, formidable confidence and the ability to produce her best tennis when the stakes are highest.

If Williams battled any anxiety over how she’d be received by the crowd, the media or tournament officials, the secret was well kept. She betrayed no extraneous emotion or movement but was utterly efficient on court as she blasted 22 winners while committing 10 unforced errors.

The same could not be said of French Open champion Li Na. She sprayed the court with 54 unforced errors to essentially hand Romanian teen Simona Halep the biggest victory of her career. Halep hit just five winners in bouncing Li from the tournament, 6-2, 7-5.

It wasn’t only Li’s mistake-prone play that stood out but her lack of intensity and joy — qualities that were so evident less than three months ago on the red clay of Roland Garros, where she made history by becoming the first Asian player to win a Grand Slam singles title.

Li, 29, didn’t hide her disgust afterward. She used an expletive to describe her performance and confessed that her confidence is gone since winning the French Open.

“I really want to do well after Roland Garros, but, you know, I mean, it’s not easy to do,” said Li, whose popularity in China is eclipsed by only Yao Ming and who, according to Bloomberg news services, has signed endorsements deals worth $42 million. “Now I even lose all the confidence on the court. I was feeling [today], ‘Oh, tennis just too tough for me.’ ”

Li’s defeat leaves the U.S. Open women’s field without any of the four reigning Grand Slam champions.

Wimbledon champion Petra Kvitova was an equally misfiring mess on Monday. She committed 52 unforced errors in her first-round defeat. And Clijsters, the reigning Australian Open champion and two-time and defending U.S. Open champion, is sidelined by an abdominal injury.

Against this chaotic backdrop, top seed Caroline Wozniacki breezed into the second round with a 6-3, 6-1 victory over Nuria Llagostera Vives.

While Wozniacki has held the world’s No. 1 ranking for 46 weeks, she’s not expected to win the U.S. Open. This is the fifth consecutive Grand Slam event in which the 21-year-old Dane has been the top seed, but she has yet to reach the finals of any of them.

Tuesday she was asked yet again about her lack of a major title.

“I know that everyone has to write their stories, but I think it’s — we should move on,” said Wozniacki, whose steady but unspectacular tactics appear to please no one but herself. “Ask me about something else, something more interesting.”

Also Tuesday, men’s top seed Novak Djokovic rolled into the second round after a 44-minute workout against Irish qualifier Conor Niland, who retired with food poisoning. Djokovic showed no trace of the shoulder pain and fatigue that forced him to retire from a championship match against Andy Murray two weeks ago in Cincinnati.

“I’m not really tired, you know, because I switched to the mode of Grand Slam focus,” said Djokovic, who has compiled a 57-2 record this year.

Defending champion Rafael Nadal prevailed on stubbornness rather than skill; he dug out of deficits in the second and third sets to defeat Andrey Golubev 6-3, 7-6 (7-1), 7-5.

The Washington Kastles were honored for their 2011 World TeamTennis championship and unbeaten season during ceremonies on Ashe before the evening’s final match.