Serena and a tournament of firsts — how this year's U.S. Open made history

The U.S. Open tennis tournament ended Sunday and history was made, as several competitors broke ground as the firsts, while 27-year veteran Serena Williams punctuated her career by participating in what is thought to be her last match.

Serena Williams may bid the sport farewell

Williams, a 23-time Grand Slam winner, said in August that she will likely be "evolving away" from tennis after this year's U.S. Open, but stopped short of saying she would retire. On Sep. 2, she was defeated by Ajla Tomljanovic 7-5, 6-7 (4), 6-1 in the third round.

"Clearly, I'm still capable. ... (But) I'm ready to be a mom, explore a different version of Serena," she said. "Technically, in the world, I'm still super young, so I want to have a little bit of a life while I'm still walking."

When asked if she would consider coming back to the sport, she said, "I don't think so, but you never know."

Carlos Alcaraz is the youngest to be ranked No. 1 in men's tennis

Carlos Alcaraz, of Spain, defeated Casper Rudd 6-4, 2-6, 7-6 (1), 6-3 in the final round of the U.S. Open Sunday, earning his first Grand Slam title and becoming the youngest man to be ranked No. 1 in the world at 19 years old.

This year's U.S. Open is Alcaraz's eighth major tournament appearance.

Frances Tiafoe is the first American man to reach the semifinals in years

Frances Tiafoe, from Maryland, became the first American man to make it to the semifinals of the U.S. Open in 16 years.

He defeated veteran Rafael Nadal in the fourth round before beating Andrey Rublev 7-6 (3), 7-6 (0) last Wednesday. Though Tiafoe was eliminated by Alcaraz Friday.

The last American man to reach the U.S. Open semifinals was Andy Roddick, who was eliminated by Roger Federer in 2006. Roddick is also the last American man to win a Grand Slam singles tournament since winning the U.S. Open in 2003.

Ons Jabeur is the first African and Arab woman to reach the finals

Ons Jabeur of Tunisia became the first African and Arab woman to reach the finals at the U.S. Open.

She beat Caroline Garcia 6-1, 6-3 on Sept. 9, marking her second consecutive appearance at a Grand Slam title match. She was also a finalist at Wimbledon two months ago.

Automation's role in deciding out-of-bounds balls

At this year's U.S. Open, technology showed it was up for the job.

Optical technology made the decisions at the U.S. Open matches, as reported by NPR's Melissa Block.

Immediately after impact, a recorded voice shouted out the call: "FAULT!" for a wayward serve; "OUT!" for a ball that lands long or wide in a rally.

By replacing human line judges with the optical system called Hawk-Eye Live, "we're providing the players a fairer playing field with a lot more integrity, a much higher accuracy call," says Sean Cary, who oversees officiating for the United States Tennis Association (USTA), which runs the U.S. Open.

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