US Open Tennis 2018 Women's Final: Winner, Score and Twitter Reaction

Japan's Naomi Osaka pulled off a historic victory in her first Grand Slam championship event by beating Serena Williams in straight sets at Arthur Ashe Stadium in Flushing Meadows, New York, but controversial penalty calls by chair umpire Carlos Ramos took some of the luster away from the occasion.

Osaka showed excellent power and consistency during her 6-2, 6-4 victory over the 23-time Grand Slam winner, and her dominant play in the first set put Williams in a come-from-behind position.

While Williams played better in the second set, Ramos warned her for receiving coaching from the stands, a "code violation," and then took a point away from her after another violation for smashing her racket.

Williams was upset by the call, and she berated Ramos between games. She called him a thief, and Ramos responded by leveling a one-game penalty for her accusation.

"You stole a point from me. You're a thief, too," Williams said, per ESPN.com.

Williams' coach, Patrick Mouratoglou, admitted during an on-camera interview with ESPN's Pam Shriver that he was giving his player advice but that he had never received a code violation for that in the past.

Longtime tennis writer Ben Rothenberg tweeted that he thought the actions of the Williams team warranted the penalty.

Shortly before Williams took the court for the final game of the match, she was sitting in her courtside chair and crying.

The largely pro-Williams crowd cascaded boos down as the penalty was announced and after the match was over, making for a bizarre awards ceremony. Both players seemed embarrassed and taken aback, and Williams asked the crowd to stop booing and recognize Osaka for her championship performance. She also attempted to comfort the 20-year-old champion.

The ceremony was also an awkward moment for Osaka, and she seemed apologetic for beating Williams, whom she has said is her tennis idol.

"I know that everyone was cheering for her and I'm sorry that it had to end like this. I just want to say thank you for watching the match. Thank you," said Osaka, per ESPN.com. "It was always my dream to play Serena in the U.S. Open finals so I'm really glad that I was able to do that. I'm really grateful that I was able to play with you."

Osaka is the first Japanese player to win a Grand Slam title. She was sharp at the start of the match, reeling off five consecutive games after Williams won the first game on her serve. It was clear that Osaka was not intimidated by competing against her rival.

Williams seemed to pick up her play in the second set, but Osaka refused to give in, and the penalties issued by the chair umpire appeared to knock Williams off stride.

After the match, Williams compared her behavior to those of men who competed in the tournament and had acted out, and she said that they had not received similar penalties.

Williams has had recent problems at the U.S. Open, as she lost in the semifinals in 2015 and '16. She also did not play last year because of her pregnancy.

Osaka was victorious in her first Grand Slam final, and she earned $3.8 million for the triumph.