- Naomi Osaka, 20, beat Serena Williams, 36, to win the US Open on Saturday.
- On Monday, the newly crowned champion appeared on the "Today" show to discuss the highly contentious final.
- The chair umpire took a game away from Williams in the second set after she got into an argument with him over earlier penalties.
- The trophy ceremony featured a chorus of boos, causing Osaka to cry and tell the crowd, "I'm sorry it had to end like this."
- Osaka said on the "Today" show that she felt as though she had to apologise for beating Williams because it was so emotional in the stadium.
The mood at Arthur Ashe Stadium turned bitter on Saturday night after Williams was penalised for receiving coaching, slamming her racket, and then getting into an argument with the chair umpire, which cost her a game in the second set.
Osaka, 20, from Japan, went on to win the match in straight sets, 6-2, 6-4.
During the trophy ceremony, Osaka was asked what it felt like to beat Williams, 36, a player she's idolized her whole life. She declined to answer, saying only, "I'm sorry it had to end like this."
When asked on Monday why she apologised, Osaka said the match and the mood in the stadium made her emotional.
"I just felt like everyone was sort of unhappy up there," she said on the "Today" show. "I know that it wasn't really - the ending wasn't how people wanted it to be. I know that in my dreams I won in a very tough, competitive match. I don't know. I just felt very emotional. I felt like I had to apologise."
Osaka also spoke about what it felt like to have her trophy ceremony marked by a chorus of boos. During it, a tearful Osaka covered her face with her visor.
"I felt a little bit sad, because I wasn't really sure if they were booing at me or if it wasn't the outcome that they wanted," she said. "I also could sympathize, because I've been a fan of Serena my whole life, and I knew how badly the crowd wanted her to win."
The booing got so loud that at one point Williams put her arm around Osaka and offered words of encouragement, something Osaka on Monday said made her feel "really happy."
Williams also told the crowd to stop booing and to celebrate Osaka's win.
As for her thoughts on the drama that unfolded between Williams and the chair umpire, Osaka said she hadn't done enough research to give a full opinion.
"For sure I want to watch everything, and I want to know what happened, because this is sort of one of the biggest things that happened to me," Osaka said.
Osaka said that during the arguments on the court, she had her back turned and didn't hear anything until the penalty was announced.
"I was a little bit confused throughout the whole thing," Osaka said.
In addition to the in-game penalties, Williams was fined $US17,000 by the tournament's referee office for her on-court outbursts.
Many in the tennis community have called Williams' punishment evidence of a double standard in the sport.
"When a woman is emotional, she's 'hysterical' and she's penalised for it. When a man does the same, he's 'outspoken' and there are no repercussions," the 39-time Grand Slam winner Billie Jean King tweeted on Saturday.
Watch Osaka's full interview on the "Today" show: