Serena Williams told Naomi Osaka she was proud of her after the Japanese stars US Open win. — Serena Williams told Naomi Osaka she was proud of her after the Japanese star's US Open win.

Tokyo, September 13: Naomi Osaka revealed Serena Williams told her she was proud of her after she claimed the US Open title.

How do I feel as US Open winner? Tired, says Osaka

Osaka, 20, became the first Japanese player to win a Grand Slam with her 6-2, 6-4 win over her idol Serena in the final on Saturday.

However, her success was overshadowed by controversy surrounding Serena, who was handed three code violations by Carlos Ramos before accusing the umpire of sexism.

Osaka said she was unsure just why the crowd were booing at the time, but Serena had some kind words for the champion.

"She said, like, she was proud of me and that I should know that the crowd wasn't booing at me," Osaka told The Ellen DeGeneres Show. "So I was really happy that she said that.

"At the time, I did kind of think they were booing at me 'cause I couldn't tell what was going on because it was just so loud in there, so it was a little bit stressful."

As Serena fell apart, Osaka showed maturity by staying cool to close out her first maiden title.

Osaka said she was taught as a youngster to ignore the other side of the court.

"You're told to just turn around and try to focus so I tried to do that," she said. "But in my mind, I really wanted to know what was going on."

Nissan brand ambassador

Meanwhile, Japanese automaker Nissan Motor Co (7201.T) said it had signed Osaka as its next brand ambassador, tapping the tennis star's youth, drive and Japanese roots to appeal to younger customers.

"Growing up, my dad drove a Nissan, so being able to be a brand ambassador now, it feels like I've come full circle," Osaka said at a contract signing event at Nissan's headquarters in Yokohama.

Nissan said the passionate video-game player and Beyonce fan would appear in global promotions and advertising as part of its three-year contract, in something of a branding departure for a company whose popular GT-R sports car appeals mainly to men aged 40 and older.

Nissan joins a growing number of companies which have enlisted Osaka for endorsement, including adidas AG (ADSGn.DE), Yonex Co (7906.T), Nissin Foods Co (1475.HK), Wowow Inc (4839.T) and Citizen Watch Co (7762.T).

(With inputs from OPTA and other Agencies)