"I was nervous, but I did my best, and I'm super proud of myself," Lee told reporters after the competition. "It's crazy. I didn't ever think I'd be here."
Lee's win is the fifth Olympic gold in a row for the United States in the individual all-around. Team USA's dominance in the sport was called into question after the Russians took gold in the team event two days ago.
Brazil's Rebeca Andrade took silver, winning the first ever medal for her country in women's artistic gymnastics. Angelina Melnikova, a veteran of the team from Russia, took bronze.
After her win, Lee smiled and hugged her teammate Jade Carey, who placed eighth.
After Biles withdrew, Lee, an 18-year-old from Minnesota, became the highest-qualifying U.S. gymnast for the all-around final. Each country is allowed to send a maximum of two gymnasts to the event.
Lee said that as she went into the final, she tried not to think about suddenly having a real shot at gold. "This whole season I've been second to her. So I just did what I do best, didn't focus on it, though, because I knew I'd get in my head."
Team USA called on Carey, who had the next-highest score in the qualifiers, to step in as the second U.S. gymnast. Carey, a 21-year-old from Arizona, took an unusual path to the Olympics – she qualified in individual international competitions and wasn't part of the four-member group that competed in the team event.
Carey came to Tokyo as an event specialist in the vault and floor exercise.
Twenty-four gymnasts took part in the all-around final, and each will compete in the four events: uneven bars, balance beam, floor exercise and vault.
Brazil's Rebeca Andrade dominated the vault, followed by Jade Carey
Carey scored a 15.200 in a vault with a very high degree of difficulty — a tenth of a point behind Andrade.
Lee smiled after landing her vault and scored a very solid 14.600. Melnikova scored slightly higher than Lee with a 14.633. Their vaults had the same degree of difficult but Melnikova's execution score was better.
Sunisa Lee proved again that she's amazing on the uneven bars
Lee has become famous for her exceptional uneven bars routines. She proved her skills in the event once again Thursday, beating all other medal contenders with a routine with the highest degree of difficulty. She scored a 15.300.
"I just told myself to just do what I normally do, because when I was kind of getting in my head, I was messing up my bar routine a little bit," she said later. "This week has not been easy on bars but I pulled myself together and I just stayed focused."
Derwael, Lee's chief rival on the uneven bars, scored just below her with a 15.266.
Carey fell during warmups for the uneven bars, and her competition score, 13.500, was the lowest of the top group.
Russia's Vladislava Urazova pulled off the top balance beam score
Vladislava Urazova from the Russian team had the top score on the balance beam, at 14.200, but Lee delivered a strong enough routine to take the overall lead with a 13.833.
Carey fell off the 4-inch-wide balance beam during her routine and ended up with a score of 11.533, dashing her hopes of getting on the podium.
Lee's floor routine cements her win
Lee's 13.700 floor routine was enough to seal her place in the history books. It wasn't the highest-scoring one of the night — that was from Japan's Mai Murakami — but it was what Lee needed to win gold.
The floor is not considered Lee's strongest event. She had not been slated to do it during the team final two nights ago but stepped in when Biles pulled out.
After the U.S. gymnasts won silver in the team event, Lee tweeted, "we do not owe anyone a gold medal, we are WINNERS in our hearts."
On Thursday, she proved that yet again, gold medal in hand.
NPR's Mandalit del Barco contributed to this report.
ARI SHAPIRO, HOST:
American gymnast Sunisa Lee is now the Olympic gold medal winner in the all-around gymnastics final. As NPR's Mandalit del Barco reports from Tokyo, she won the individual competition, the same one Lee's teammate, Simone Biles, withdrew from citing mental health concerns.
MANDALIT DEL BARCO, BYLINE: Simone Biles was in the stands of Tokyo's Ariake Gymnastics Centre cheering on Sunisa Lee as she did a difficult routine on the uneven bars and when she was on the balance beam executing what's called a wolf turn, crouching with one leg straight out and turning. Biles cheered when Lee made a fine landing off the vault then finished up with a floor routine filled with difficult flips and jumps.
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SUNISA LEE: It just is so surreal, and I haven't even let it sink in yet. Like, it doesn't even feel like real life (laughter).
DEL BARCO: After she got her gold medal, Lee told reporters she'd been super nervous, but Biles gave her a pep talk.
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LEE: I was starting to put a little bit too much pressure on myself. Knowing that Simone was gone, I feel like people kind of put that pressure on me that I had to come back with a medal. So I try not to think about it. And that's what they told me to do, to just focus on myself and do what I normally do because that's when I compete the best.
DEL BARCO: Lee is 18 years old, from St. Paul, Minn., the first Hmong American to make a U.S. Olympic team. She also just came off a difficult time personally. Two years ago, her father was paralyzed after he fell from a tree. Then, her aunt and uncle died of the coronavirus. The pandemic lockdown kept her from working out at her gym. And when she returned, she badly injured her ankle.
(SOUNDBITE OF ARCHIVED RECORDING)
LEE: Yeah, the past two years have been absolutely crazy with COVID and just my family and everything else. This medal definitely means a lot to me because there was a point in time where I wanted to quit. And I just didn't think I would ever get here, including injuries and stuff. So there are definitely a lot of emotions, but I'm super proud of myself for sticking with it and believing in myself.
DEL BARCO: Lee is now the fifth American in a row to win an Olympic gold medal in the individual all-around competition. She follows Biles, Gabby Douglas and their predecessors starting in 2004. Brazilian silver-medalist Rebeca Andrade is the first woman to earn a medal in women's artistic gymnastics for her country. Angelina Melnikova, from the Russian team, took the bronze. Next week, Suni Lee and the other medalists plan to compete in the finals of the individual gymnastics events. Simone Biles qualified for those too, but she hasn't yet said if she'll compete.
Mandalit del Barco, NPR News, Tokyo. Transcript provided by NPR, Copyright NPR.