The Russian has struggled to find form this season, crashing out of the Qatar Open in the opening round.
For Sharapova this loss is another reminder that it's back to the drawing board for the Russian as she makes her way back from a 15-month drugs ban.
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Ireland have taken a huge leap towards the title with today's win and will now watch the England v France clash with eagle eyes. But that was a mistake because if you do that in tests you can easily lose control.
Sharapova's world ranking of No.41 forced her to play a first-round match in the tournament she has won twice. "I was just really honored to play her".
Two American teenagers advanced to the second round. The 16-year-old Anisimova, who earned a wildcard into the main draw, is the US Open junior champion.
"It's very exciting. I've worked really hard for this so I'm proud of myself", Anisimova told Tennis Channel, adding that adjusting to the senior ranks had been more mental than physical. The biggest thing (in the pros) is about being tougher mentally.
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For example, if you press down hard enough on ice-I, it will transform into ice-II, which has a rhombohedral structure. But for obvious reasons, it has proven impossible to find a naturally occurring sample of ice VII at the surface.
"Of course, I wanted to do well here, and not just because I won this event a couple of times, but that's the mentality I have as a former champion, as someone that's a competitor that wants to do well and compete well at an event no matter what event it is or where it is".
Bouchard also departed in her opener, while Samantha Stosur and Belinda Bencic were among the winners.
She suffered early breaks in both sets, fought back but came up short on the key points in a performance that saw her commit six double faults and lose five service games to world No. 44 Osaka.
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As that supporter ran back towards the stands two more came on, with home defender James Collins eventually ushering them away. The Hammers return to Premier League action on Saturday 31 when Southampton are the visitors to the London Stadium (3pm).
Osaka then managed to hold for 5-4 before breaking her opponent for the fifth and final time as Sharapova found the net to hand Osaka the second set and the match.