The new US Open champion, Naomi Osaka, has spoken about the mixed emotions she felt after winning her first grand slam in a match overshadowed by an umpiring controversy.

Osaka beat her childhood idol, Serena Williams, in straight sets on Saturday but the American was penalised a game after calling the umpire a “thief”. Boos poured down from the stands at Arthur Ashe Stadium as Williams argued with the umpire, who she believed was treating her differently from male players.

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“I felt a little bit sad because I wasn’t really sure if [the crowd] were booing at me or if it wasn’t the outcome that they wanted,” said Osaka on Monday in an interview with NBC’s Today. “I also could sympathise because I’ve been a fan of Serena my whole life. And I knew how badly the crowd wanted her to win, I don’t know, I was just really emotional up there.”

The 20-year-old apologised after the match, and on Monday said she felt like the crowd had not got the ending they wanted. “I felt like everyone was sort of unhappy up there and I know that it wasn’t really … the ending wasn’t what people wanted it to be,” she said. “In my dreams, I won in a very competitive match so I don’t know, I just felt very emotional and I felt like I had to apologise.”

During the post-match interview, Williams urged the crowd to appreciate Osaka’s efforts after she had dominated the former world No1 for most of the afternoon. Osaka said she was grateful for Williams’s efforts. “I felt really happy because she knew I was crying and she was saying some things and it just made me happy over all,” said Osaka, who has lived in America most of her life but represents the country of her birth, Japan.

TODAY (@TODAYshow) “I just felt very emotional, and I felt like I had to apologize.” @Naomi_Osaka_ on why she apologized during the trophy ceremony pic.twitter.com/72UBkYw3YO

Osaka became the first Japanese player to win a grand slam singles title, and has been widely praised in Japan since her win. She added that she is still getting used to her status as a grand slam champion. “It still feels a little bit surreal, but I think it’s slowly sinking in,” she said.