However, as she struggled to keep pace with Osaka - who came into the match with a stunning 31-0 winning record this season when taking the first set - Williams was handed a point penalty for breaking her racquet. When she realised that the next game had started with Osaka ahead 15-love, Williams told Ramos he should have retracted the initial warning for coaching. But Williams played a poor game right after that to get broken immediately, and she smashed her racket on the court, destroying it.
"You definitely can't go back in time but I can't sit here and say I wouldn't say he's a thief because I thought he took a game from me", Williams said.
The US Open umpire slapped Williams with her first penalty - accusing her of being illegally coached from the stands.
Williams was up 2-1 on the changeover when she spoke again with Ramos appearing to smooth things over, and she finally found a way to break Osaka for a 3-1 lead. "Coaching on every point should be allowed in tennis. I just want to say thank you for watching the match". Honestly, there's a lot I can learn from her from this match.
Despite the controversy there were many messages of support for Osaka, who became the first Japanese grand slam victor.
But the game will be remembered for Williams' meltdown and confrontation with the umpire and match referee.
So when she had actually done it, beating Williams 6-2, 6-4 on Saturday night to become the first Grand Slam singles champion from Japan, why was it so hard?
The penalty lost Williams the title.
But Osaka - who displayed not only a stellar game but remarkable poise throughout - held serve to seal a historic win for her country.
US charges govt-linked North Korean in WannaCry, Sony hacks
There has been no communication between the USA and North Korean government about a possible extradition, the official said. A logo is pictured outside Sony Pictures Studios in Culver City, California December 19, 2014.
"She really wanted to have the 24th Grand Slam, right?" Osaka, 20, would become the youngest U.S. Open champion since Maria Sharapova was 19 in 2006.
Matches on outer courts that were affected by rain were to be moved indoors.
Ramos, the chair umpire, has a history of being a stickler.
Williams had also been the target last month of a new rule at the French Open banning catsuits like the one she wore earlier this year.
Of the five main draw finals, four will have been chaired by a female umpire this year.
She and her Reddit co-founding boyfriend, Alexis Ohanian, had a baby previous year.
Serena Williams' loss at the US Open was dramatic for all the wrong reasons in terms of sports, and critics are voicing concerns about gender double standards in terms of conduct on the court. Murray had three other Grand Slam mixed doubles titles.
Some social media users urged male tennis players to back Serena Williams.
Those in attendance began to boo, at which point Williams lifted a hand towards the crowd to quieten them before unleashing another furious volley in Ramos 'direction. She had four operations following the birth of her daughter, Olympia.
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