Despite everything that Serena Williams has won and done, her sense of self can still fluctuate based on the outcome of a particular match.

Doesn't always seem to matter that she owns a record-tying 22 major singles titles heading into the U.S. Open, which begins Monday with a retractable roof at Arthur Ashe Stadium for the first time.

Not necessarily a big deal to her that she's spent the past 3½ years entrenched at No. 1 and is the oldest woman ever to top the WTA rankings.

And there are times when the 34-year-old American basically forgets that she transcends her sport and has become a cultural icon away from the tennis court.

Williams is devastated when she is dealt a setback, such as last year's "Did that really happen?!" loss to Roberta Vinci in the U.S. Open semifinals, ending an attention-grabbing, pressure-piling bid for the first calendar-year Grand Slam by anyone in more than a quarter-century. Williams acknowledges she measures herself constantly.

"Unfortunately, I definitely do, which I don't think is normal. I definitely feel like when I lose, I don't feel as good about myself," she said.

"But then I have to, like, remind myself that: 'You are Serena Williams!' You know? Like, 'Are you kidding me?'" Williams continued, laughing and leaning forward. "And it's those moments that I have to just, like, come off and be like, 'Serena, do you know what you've done? Who you are? What you continue to do, not only in tennis, (but also) off the court? Like, you're awesome.' That really just shows the human side of me. I'm not a robot."

She is at the stage of her career where history is in the offing nearly every time a racket is in her right hand. So while the stakes are different from what they were at Flushing Meadows in 2015, Williams does have something significant to play for yet again.

After equaling Steffi Graf for the most Grand Slam titles in the professional era (which dates to 1968) by winning Wimbledon last month, Williams now can break that tie by earning No. 23 in New York. Only Margaret Court owns more major singles trophies, with 24, but more than half of that total came against amateur competition.

Not that Williams was immediately ready to think about topping Graf after pulling even with her at the All England Club.

"One thing I learned about last year is to enjoy the moment," Williams said. "I'm definitely going to enjoy this."

Good thing, too, because not everything has gone smoothly since that most recent triumph. Slowed by a bothersome right shoulder, Williams lost in the third round of singles and first round of doubles at the Rio de Janeiro Olympics — she was a 2012 gold medalist in both events — and then pulled out of a hard-court tuneup event in Ohio.

Williams is assured of remaining at No. 1 until the end of the U.S. Open, which will bring her current streak to 186 weeks in a row, tying another mark held by Graf. Depending on what happens in the tournament, Williams could be overtaken in the rankings by No. 2 Angelique Kerber (who beat Williams in the Australian Open final in January), No. 3 Garbine Muguruza (who beat Williams in the French Open final in June) or No. 4 Agnieszka Radwanska.

"It's definitely intriguing," Roger Federer said about tracking the women vying for No. 1. "It's nice to see this race."

Federer, who won five of his men's record 17 Grand Slam titles in New York, will be sitting out the U.S. Open for the first time since 1999 as he takes the rest of the season off to let his left knee heal. A year ago, Federer lost in the final at Flushing Meadows to Novak Djokovic. In Federer's mind, the top-ranked Djokovic is the favorite this time, even though No. 2 Andy Murray's summer has been "phenomenal."

One reason: Federer thinks the installation of the new $150 million roof at the main arena will limit the wind even when it's open, which will help Djokovic.

Not too long ago, Djokovic appeared to be close to unbeatable no matter the surface or conditions, and a buzz was building about whether he could chase a true Grand Slam. But he exited Wimbledon in the third round, then the Olympics in the first round, while Murray won both of those titles.

"Novak, obviously, the last two years, really, has played amazing tennis. His consistency — what I've done for, like, the last four months, he's been doing for, like, the whole year," Murray said. "So I need to try and keep that going, and the U.S. Open is always the next big goal."

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AP Sports Writer Rachel Cohen contributed to this report.

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Follow Howard Fendrich on Twitter at http://twitter.com/HowardFendrich