Wasn’t it a few years ago that tennis pundits were questioning Serena Williams’ staying power, suggesting she didn’t take the game seriously enough, that her outside interests would prevent her from reaching her potential, that she didn’t have the fitness or tennis drive necessary to keep up with the young, hungry players rising up the ranks?

Well, here she is, arriving at the Sony Open in Key Biscayne as the No. 1 player in the world at age 31, the oldest No. 1 since the WTA rankings began in 1975. She broke the record previously shared by Martina Navratilova and Chris Evert, who were 30 when they were ranked on top.

Consider that Williams’ pro career has spanned three decades. She won her first title in 1999 at age 17.

Williams is coming off a year in which she went on a 26-1 run to win Wimbledon, the Olympic gold medal and the U.S. Open, bringing her Grand Slam title total to 15. She became the first 30-year-old woman to win the U.S. Open since Navratilova in 1987 and the first woman to surpass $40 million in earnings.

Making it all the more remarkable is the fact that Williams was off the tour for 10 months between the summers of 2010 and 2011. She cut her feet on broken glass at a restaurant in Germany a few days after winning the 2010 Wimbledon title and required two operations on her right foot, which remained in a cast much of the year.

She then developed blood clots in her lungs and had a few scary visits to the emergency room.

“There were times I thought the hill seemed nearly impossible to climb,” Williams said by phone last week. “During that whole time, I wasn’t even thinking about reaching No. 1 again. Wasn’t thinking about tennis. I was just thinking about getting up out of bed. Then, when I came back in the summer of 2011, I started playing really, really well. I thought, ‘OK, I can play tennis again.’

“I started setting short-term goals. Get back to the top 10. Pass this person. Be the best American. Little by little, I climbed my way back. It feels good to be No. 1 again. I feel I should be here.”

ESPN commentator Patrick McEnroe is not surprised Williams is still around, and sitting atop the women’s game again.

“I remember four or five years ago, sitting on the set at the French Open, when Serena was making one of her many comebacks, and I got the sense she was serious about tennis, was going to commit, and I said at the time that she is capable of having a second part of her career like Andre Agassi did,” McEnroe said. “Technically, Serena’s a great player. She hits as clean as Agassi, has all the weapons, a great serve, she’s a great competitor. She just had to commit to being in shape and play enough tournaments to keep her ranking up.

“When she’s on, there aren’t many players who can stay with her. Injuries are the only thing that could keep her back.”

Williams has not abandoned her outside interests and still likes to have fun. She recently posed for a glamour photo leaning on a Bentley outside the St. Regis hotel in New York. She was in Chicago on Feb. 28 with First lady Michelle Obama and Nike executives for a program to get schoolchildren more active.

On March 1, she made headlines when she was scolded by a security guard as she tried to snap a photo of Tiger Woods from the gallery at the Honda Classic in Palm Beach Gardens.