Bianca Andreescu reacts after defeating Serena Williams in the women's singles final of the U.S. Open on September 7, 2019.Charles Krupa / AP

Bianca Andreescu is a 19-year old tennis player with many noteworthy qualities. She exhibits a level of swagger that belies her age. She is the rare player who can overwhelm opponents with either dazzling displays of power or deft touch. But by defeating Serena Williams, one of the most decorated practitioners of the sport ever, in today’s U.S. Open women’s singles final (6–3, 7–5), Andreescu proved that her most noteworthy quality is the composure she displays in pressure-packed moments when other players might crumble.

Up 5–1 in the second set, Andreescu had an opportunity to serve out the match and claim her first Grand Slam singles trophy. She had been in control from the onset, having consistently outmaneuvered the veteran standing across the net. But with the title in sight, Andreescu blinked—then blinked again. She was broken twice while serving for the match, thereby sacrificing the lead she had worked so hard to build. She became visibly unnerved by the ferocious roars of the heavily pro-Williams crowd in Arthur Ashe Stadium, the largest tennis facility in the world. After several points, she put her fingers in her ears to block out the cheers for her opponent, a gesture in contrast to her self-assured demeanor until then. When Williams leveled the match at 5–5, Andreescu appeared destined to lose a set she had once controlled, and an epic comeback seemed to be taking shape.

Then Andreescu did something surprising, considering her relative inexperience and the pressures of the moment. She composed herself in real time. She held her serve to take a 6–5 lead, then broke Williams the very next game to claim the title. In doing so, she became the first player born in the 2000s to win a Grand Slam.

Andreescu plays an aggressive brand of tennis. She’s not a counterpuncher like Simona Halep, who defeated Williams in the finals at Wimbledon in July. She looks to dictate play with her forehand, which she hits with enormous amounts of pace and topspin like Rafael Nadal, the 18-time Grand Slam champion who will face Daniil Medvedev in the men’s final tomorrow.

But in today’s final, it was the consistency Andreescu displayed that ultimately allowed her to triumph. Williams was the aggressor for most of the match; she hit 14 more winners than Andreescu, but also committed 16 more unforced errors. Williams pressed at times, often trying to find angles that weren’t there or to hit winners at inopportune points in rallies, while Andreescu showed a willingness to grind: She ran over 400 total feet more than Williams, frequently scrambling from one side of the court to the other just to keep the ball in play. It was a gritty, confident performance by a player who wasn’t even alive when Williams captured her first Grand Slam singles title 20 years ago.

Williams has now lost four Grand Slam finals in a row, and remains one title shy of Margaret Court’s all-time record of 24 major championships. For the second straight year at the U.S. Open, she lost to a precocious player with the talent to be a force on the women’s tour for years to come. Today’s final was thankfully bereft of last year’s controversy, but for Williams and her fans, the sight of her coming up short once again on one of the sport’s biggest stages is surely bittersweet. Still, the atmosphere within Arthur Ashe Stadium when she began her comeback in the second set was electric. (The support the crowd showed her was reminiscent of the way fans at this year’s Wimbledon men’s final rallied around Roger Federer in his unsuccessful bid to defeat Novak Djokovic.)

As for Andreescu, a slew of statistics speaks to the remarkable season and meteoric rise she is currently in the midst of. She has not lost a match since the Miami Open, when she retired during the fourth round due to a shoulder injury, and now has an 8–0 record against players ranked in the top 10. Last season, she lost in the qualifying rounds of the U.S. Open; this year, in her first appearance in the tournament’s main draw, she emerged victorious.

But to truly appreciate Andreescu, it’s necessary to watch her play, from the ways she strikes the ball with precision and strength to the confidence of her body language. In the early stages of today’s final, Andreescu was the more demonstrative player, punctuating winning points with fist pumps and cries of “Come on!” She withstood everything Williams threw at her, including a passing shot aimed directly at her body that Andreescu deflected at the last moment. By contrast, Williams often seemed tense, muttering to herself when points didn’t go her way and occasionally flashing looks of relief when they did. Williams fed off the crowd’s energy and briefly flirted with a comeback, but at the end of the match, Andreescu emerged the winner. There’s a good chance this will be the first of many Grand Slam victories for the young Canadian phenom.

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