Correction: An earlier version of this story incorrectly reported that Serena Williams is attempting to eclipse Steffi Graf’s record of 309 consecutive weeks at No. 1, it’s 186 consecutive weeks.

Serena Williams competing against Daria Gavrilova of Australia at the Rio Olympics. (Charles Krupa/AP)

The fundamental weapons that earned Serena Williams the first of her 22 Grand Slam titles at the 1999 U.S. Open remain in her arsenal: explosive speed, raw power, fierce determination.

Now twice as old as when she won her maiden major at 17, Williams has transformed herself into the sport’s most efficient power player. Her serves are bigger. Her rallies are shorter. She spends less time on court. She approaches the net more frequently and attacks second serves more aggressively. Her game is power — with purpose.

“She’s not all one-way traffic,” says 1978 U.S. Open finalist and ESPN analyst Pam Shriver.

This late-career refinement is why Williams, who turns 35 next month, is still atop the sport and setting records as she opens her campaign at the U.S. Open. Williams, seeking an Open-era-best 23rd major title, begins Tuesday against 36th-ranked Ekaterina Makarova of Russia, a dangerous unseeded opponent and two-time Grand Slam semifinalist.

Williams shares the record for most Grand Slam titles, at 22, with Steffi Graf. She is also attempting to eclipse Graf’s record of 186 consecutive weeks at No. 1, which she will equal regardless of her result in New York. But three players have a chance to unseat Williams during the tournament, in which case she would remain knotted with Graf.

Williams speaks to the media at the U.Sl Open on Friday. (Bryan R. Smith/AP)

Whether Williams can tap into her streamlined power could depend on her health.

She injured her right (serving) shoulder two days after winning a seventh Wimbledon in July. It hampered her at the Rio de Janeiro Olympics, where she was upset, 6-4, 6-3, in the third round by Ukraine’s Elina Svitolina. She pulled out of this month’s U.S. Open tuneup near Cincinnati and hasn’t suited up since.

“I haven’t played a lot,” said Williams, who came two matches from winning all four majors last year and finished runner-up at the Australian and French opens this season. “I haven’t practiced a lot, but I’m now starting to feel a little better.”

If Williams leaves New York with a second major of 2016, it will be in no small part a result of her increasingly effective and tactical use of pace. The change has been both subtle and radical, like a home run hitter tweaking his batting stance or a point guard altering her release point.

“Serena has said she didn’t know what she was doing when she won the 1999 U.S. Open,” said Chris Evert, who, like Williams, is a six-time New York champion. “She was programmed to hit the ball hard without any strategy. She got by because she was a great athlete with power. But now she is much smarter about her game.”

Much of the fine-tuning has occurred under the tutelage of Patrick Mouratoglou. Since teaming up with the French coach following a first-round exit at Roland Garros four years ago, Williams has won 9 of 17 Grand Slam events, the best success rate of her career.

Players to watch. Top: Angelique Kerber, of Germany; Madison Keys of the United States; Petra Kvitiova, of the Czech Republic. Bottom: Garbine Muguruza of Venezuela; Serena Williams of the United States; Venus Williams of the United States. (AP/AP)

Mouratoglou, in a recent interview, explained that his work with Williams is predicated on capitalizing on her strengths: pouncing on short service returns; moving forward to take short balls early or high balls out of the air with swing volleys; using speed and power to construct points to attack the right ball, not any ball.

“The goal has not been to shorten the point,” he said. “The goal is more to take advantage of the quality of her shots.”

He has pushed her to approach the net more, where she generally wins 70 to 80 percent of her points. And most of all, he reminds her to rely on her biggest weapon: her serve.

“The problem, and it’s a good problem to have, is that she has many weapons,” Mouratoglou said. “Sometimes she can rely on something else. She cannot forget how good a server she is, and how good her second serve is also.”

Video clips of Williams’s early finals in New York in 1999, 2001 and 2002 show how far she has come: She often fails to take advantage of court position, thus extending rallies. She rarely comes to net. Her serve has pop but is less consistently accurate or as powerful.

“She’s certainly going for her shots,” noted John McEnroe on a YouTube clip of the televised broadcast near the end of Williams’s maiden victory against Martina Hingis in the 1999 U.S. Open final. “Ton of winners, ton of unforced errors. Clearly has the makings of a great, great champion here.”

Statistics from the WTA and the tour’s analytics partner, SAP, illuminate her evolution from a basher to a basher with intent.

The mix of data pertains mostly to WTA matches and not the four Grand Slams, which are operated independently. Some data include information that SAP culls from the electronic tracking system known as Hawk-Eye. It dates only from March 2015. Some WTA data go back to 2008.

Among the findings:

●Williams’s average serve speed has gone from 90 mph to 98 mph, while her average top serve speed has increased from about 115 mph to 120 mph, meaning she is going for bigger serves and more easy points.

●Williams’s combined rally length when serving and receiving has fallen from 4.5 shots to four shots, indicating that she is ending rallies more quickly.

●Williams is spending 10 fewer minutes per match on court compared to eight years ago, dropping from about 90 minutes to 80 minutes on average. This includes both WTA and Grand Slam contests. This year she is averaging 77 minutes.

“I just feel like I try to be as efficient as I can out on the court,” Williams told reporters Friday. “That’s not always possible. But I just feel like my game has matured a lot overall, and mentally sometimes I definitely do put a little more pressure on myself than I did a long time ago.”

The statistics also show that she is covering more distance in her matches, meaning she is expending more energy by running more. Her total number of winners and unforced errors have also ticked up, with the ratio of errors increasing.

Mouratoglou says this could be because he has also tried to instill a plan B when Williams’s power game is off. “We’ve worked on being able to hit more shots if necessary,” he said.

Longtime opponents have noticed the shift.

“Now she’s more aggressive,” said No. 7 seed Roberta Vinci, 33, who slammed the door on Williams’s Grand Slam bid in last year’s U.S. Open semifinals. “The point is more quick than 10 years ago.”

Second-seeded Angelique Kerber, who defeated Williams in the Australian Open final but finished runner-up to the American at Wimbledon, did not hesitate when asked who was the most efficient power player in women’s tennis.

“When she is serving, it’s like impossible actually to break her,” Kerber said of Williams, adding: “To play against her, definitely you have to play your best.”

Shriver believes the key to Williams’s longevity at the top is a willingness to adapt, what she called a “growth-oriented mind-set.”

Some is borne of necessity, Shriver noted, because players have learned to absorb her pace with better training and the help of new string and racket technologies. “It’s made her have to use more than just the plain old Serena power,” Shriver said.

Injuries, particularly to her knees in recent years, add another dimension.

“She doesn’t have the luxury of being 20 years old and having that fresh body,” Evert said.