NEW YORK -- Bianca Andreescu defeated Serena Williams in straight sets, 6-3, 7-5, to win her first Grand Slam title in Saturday's US Open women's final. In a matchup between tennis' Canadian teenage newcomer and one of the greatest superstars in the history of tennis, the youngster took home the crown.

Despite a late rally from the 23-time Grand Slam champion, Williams fell short of making history once again in a Grand Slam final, falling short of tying Australian Margaret Court's all-time Grand Slam singles titles record. Since returning to tennis after becoming a mother, Williams is 0-4 in Grand Slam finals.

Andreescu, at just 19-years-old, showed incredible poise while playing in her first ever Grand Slam final. Andreescu's ascent to champion in the tennis world over this past season has been nothing short of incredible. Just a year ago, Andreescu was ranked outside the top 200.

Coming into the championship, Andreescu had not lost a completed match since March 2, owning an overall 38-4 record for the season. She was No. 152 in the world at the start of the year, and reached No. 15, and now with the US Open title, Andreescu is set to become No. 5. Even more impressive is the fact that Andreescu has won the first eight matches she has played against top-10 players.

"It's so hard to explain in words," Andreescu said during the awards ceremony. "I'm just beyond grateful. I've worked really, really hard for this moment. This year has been a dream come true and now being able to play on this stage against Serena, a true legend of the sport, is amazing."

Williams will turn 38 later this month, while Andreescu turned 19 in June. The Canadian teenager had not yet been born when Williams won her first career Grand Slam title, at the US Open in 1999. Saturday's final was the biggest age gap (18 years) in a women's Grand Slam singles final in the Open era, which began in 1968. It beats out last year's 16-year gap when Williams lost to 20-year-old Naomi Osaka in last year's dramatic and controversial US Open final.

In the second set, Williams kept herself alive in the championship, breaking Andreescu to pull to 2-5. Williams saved the first championship point with a forehand winner. Williams held her next serve, broke Andreescu again and held again to level the second set at 5-5. Andreescu came out to hold her serve and halt Williams' run of four consecutive games. 

At 5-6, 15-40, Williams saved another championship point with an ace. On Williams second serve, Andreescu fired a forehand winner to win the match.

The 26,000 fans in Arthur Ashe Stadium were completely energized by Williams' comeback bid, cheering loud enough to force Andreescu to try to cover her ears on the changeover. When asked what she had to overcome to get over the finish line in the post-match, on-court interview, Andreescu responded: "The crowd."

"Well, I was blocking out the noise, or trying to," Andreescu said after the win. "I could barely hear myself think really. It was really, really loud. But I guess that's what makes this tournament so special."

Andreescu hit 18 winners to 17 unforced errors, converted five of 12 break point opportunities and won 64% on her first serve. Williams struggled with unforced errors, and finished the match with 33 unforced errors to 33 winners. She also double-faulted on break points three times.

Williams played her best tennis since returning to competition after the birth of her daughter, at this year's US Open. But, she was undeniably frustrated when assessing her game after the loss.

"I love Bianca," Williams said. "I think she's a great girl. But I think this was the worst match I've played all tournament. It's hard to know that you could do better. It's just taking it ... I don't even know what to say."

"I think her returns make me play better and puts pressure on my serve. At the same time it's inexcusable for me to play at that level."

When asked about Court's record, Williams shrugged it off. "I'm not necessarily chasing a record. I'm just trying to win Grand Slams. It's definitely frustrating, you know. But for the most part I just am still here. I'm still doing what I can do."

With the win, Andreescu ties Monica Seles for the Open Era record of fastest path from Grand Slam final debut to Grand Slam final victory. Seles won the 1990 French Open in her fourth major appearance. Andreescu was ousted in the first round of her first Grand Slam appearance, at 2017 Wimbledon. That was followed by two second round exits, at this year's Australian Open and French Open. Andreescu told reporters after the win that she used visualization practice to imagine what the US Open final match would look like.

Andreescu played fearless tennis against one of the greatest tennis players of all-time, in the first Grand Slam final of her young career. It was a star-making performance from the teenager, topping off what's been an incredible rise in the sport of tennis this year. A performance reminiscent of the very opponent she faced tonight, who also broke through for her first Grand Slam title as a teenager.

"[Serena is] an inspiration to many, many people, not only athletes," Andreescu said. "She's truly a champion. I've really strived to be like her. Who knows? Maybe I can be even better."