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Now, Muguruza – at the age of 28 – is the oldest year-end champion since Serena Williams seven years ago and is up to third in the rankings.
For Muguruza it was never a question of if she had the game to be back among the elite players, merely just the need to prove so.
"I'm just very happy I proved to myself once again I can be the best, I can be the 'maestra,' like how we say in Spanish," Muguruza said. "That puts me in a very good position for next year, a good ranking.
"The last couple of years, I didn't play the same way I played before. But I didn't play bad tennis, either.
"I was just here, there, not going into the deep rounds at grand slams that made the difference. I always felt I had the tennis. I was just not putting the battle together.
"I always believe I [could make] finals of a grand slam, [climb] the rankings, I'm like 'I have the tennis, I just have to show it'. It's hard, of course."