An hour before Monday evening’s celebration to honor the 40th anniversary of the Open Era in tennis, Maria Sharapova stood outside the player’s lounge behind Arthur Ashe Stadium and received a warm welcome from Arlen Kantarian, the CEO of professional tennis for the United States Tennis Association. Sharapova greeted Kantarian, turned to her agent, and joked, “He’s giving me a wild card into the draw. I’m going to play.”

If only she could. Because of two small tears in her rotator cuff, Sharapova must sit out this year’s U.S. Open. Instead of fighting for the no. 1 ranking, she’s watching from the sidelines. Instead of trying to polish off a fine season that began with a dominating performance in Melbourne, where she won the Australian Open without losing a set, she’s headed back to Arizona for several weeks of rehab. Luckily, she won’t need surgery.

Sharapova, no matter her form, would give the women’s tournament here a jolt after a year marred by injuries and the retirement of Justine Henin, the no. 1 player. But what the U.S. Open, and for that matter the women’s tour, needs most is a player like the one we all thought Sharapova would become when she won Wimbledon as a 17-year-old in 2004. On that day, Sharapova seemed destined to follow in a long line of great champions, women such as Margaret Court, Billie Jean King, Chris Evert, Martina Navratilova, Steffi Graf, Monica Seles, Martina Hingis, the Williams sisters, and Henin, who became the first to retire with the top ranking. No one had made Serena Williams look as thoroughly ordinary as Sharapova did that day. No one had hit the ball so hard so consistently.

Sharapova has had great moments since then, but she’s never remained healthy enough to take command of the tour. Will she ever? Will anyone ever? At the end of this tournament, any one of five players could be crowned no. 1. Who is the next leader of the pack?

Ana Ivanovic, 20, is the most obvious candidate. She’s solidly built and dedicated (her fitness is much improved in the last year) and has no glaring weaknesses. She won her first major title earlier this year at the French Open and, perhaps most important of all, on a tour where attendance by top players is at best spotty, she hasn’t suffered from a lot of injuries until a recent problem with her thumb caused her to skip the Olympics.

Ivanovic has the attitude of a no. 1 player and an evolving, entertaining style: She volleys a lot more than she once did and looks to pounce whenever she can. If you saw her struggle during her first-round victory yesterday over Vera Dushevina, 6-1, 4-6, 6-4, you saw the characteristic that is both her best asset and her worst liability: intensity. Despite playing just two matches since her early defeat at Wimbledon (because of her thumb) Ivanovic expected to win every point yesterday. That’s healthy for a would-be champion. Unfortunately — and this is the trouble with intensity — she pressed and rushed, and at times tried to do too much when the match became tense.

Ivanovic blamed her recent injury on eagerness. She took a break after a disappointing Wimbledon and returned to the court with a lot of motivation, so much that she pushed herself too hard too soon. In the next few months that followed, she spent more time with doctors than she did hitting tennis balls. Eventually, after a several visits that included a trip to her doctor in Australia from Beijing, Ivanovic found the cause of the pain that at one point prevented her from holding a racket: cysts. She played without pain for the first time last Monday, when she began practicing for this tournament.

Ivanovic is not the kind to slack off, or become depressed, because she can’t swing a racket. She’s cheerful to the point of exuberance after first round victories, a few hours on the practice courts, or even losses in major finals (after she lost to Henin in Paris last year, Ivanovic gave a remarkably upbeat press conference). When she had to withdraw from the Beijing Olympics, she ran sprints and kept up her fitness as best she could.

“We were making jokes at the Olympics that I should try to compete in something else because I was just doing running and sprints,” she said.

Ivanovic doesn’t expect to play like a no. 1 seed at this tournament — that, she said, might be “a lot to ask” considering how little practice, and how few matches, she has played this summer. Eventually, though, she wants to be the woman to beat, even when Sharapova gets off the red carpet and back onto the court. She has the skill, and the desire, to do it. Maybe not long from now, her time will come.

***

American Sam Querrey is known for his big serve, but yesterday he decided to receive, rather than serve, when he won the coin toss before his match with Tomas Berdych, the no. 22 seed. Querrey might make a habit of returning first after scoring the biggest upset of the afternoon yesterday, a 6-3, 6-1, 6-2 drubbing.

In a more mild upset, Tommy Haas outlasted Richard Gasquet, seeded no. 12, in five sets, 6-7(3), 6-4, 5-7, 7-5, 6-2. On the women’s side, Gail Brodsky of Brooklyn, profiled in these pages last week, didn’t win her first U.S. Open match, but she did herself proud in a 7-5, 6-3 defeat against Agnes Szavay, seeded no. 13.

Mr. Perrotta is a senior editor at Tennis magazine. He can be reached at tperrotta@ tennismagazine.com.