Tennis fans erupt over Naomi Osaka act during Serena Williams match

The tennis world has erupted after Naomi Osaka was spotted cheering on Serena Williams against Emma Raducanu only hours after losing her own match at the Cincinnati Masters.

Williams is playing one of her last competitive tennis matches in her illustrious career after announcing her retirement at the Canadian Open last week.

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The 23-time grand slam champion was knocked out of the Canadian Open in the second round and was up against the next generation of tennis stars in World No.10 Raducanu.

Raducanu got off to a flying start in the first round encounter after racing to a 4-1 lead.

Williams was attempting to draw energy from an electric crowd as she fought her way back into the first set.

And during the applause, four-time grand slam champion Osaka was shown high-up in the crowd cheering on Williams.

Osaka often points to Williams as her childhood tennis idol.

And fans were quick to praise the beautiful moment of Osaka cheering on her idol in what will be one of Williams' last matches on the WTA Tour.

Raducanu ended up running away with the match 6-4, 6-0.

Last week, Osaka expressed her disappointment that her childhood idol announced she was ready to step away from the sport.

"Today is just really not a good day," Osaka said on Twitter.

The four-time grand slam champion has made it no secret that Williams was her tennis idol growing up.

Osaka famously took a selfie with Williams on her WTA Tour debut in 2014.

Naomi Osaka knocked out of Cincinnati Masters

Earlier, Naomi Osaka suffered a major setback before the US Open after a day of drama at the Cincinnati Masters.

Osaka bowed out in the first round in Cincinnati going down in straight sets.

While fan favourite Coco Gauff suffered an injury that leaves her US Open hopes hanging in the balance.

Gauff called for a trainer to check out a leg complaint when she was 5-3 up in the opening set against Marie Bouzkova and looking likely to clinch the opening stanza.

However, the 18-year-old's movement was clearly hampered and Bouzkova capitalised to storm back and claim the opener 7-5.

Gauff bravely tried to play through the pain but lasted just one game into the second set, before being forced to retire from the match.

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