You never know how you'll react when you're on top. Garbine Muguruza ascended to the No. 1 spot at the US Open and is playing her first event as the world's best player in Tokyo this week.

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The 23-year-old got off to a solid start, taking out Rio Olympic gold medalist Monica Puig, 6-4, 6-0. She then dispatched Caroline Garcia, 6-2, 6-4 to reach the semifinals.

"I think I'm more the favorite, I guess," Muguruza said about being No. 1. "But, I'm trying to just go out there and fight, and play—give everything I have. That's what counts."

Muguruza is looking to extend her lead over world No. 2 Simona Halep. She's only 150 points ahead of the Romanian, who's not playing this week.

The in-form Spaniard next faces Caroline Wozniacki for a spot in the final.