Over the course of the next three years, the Spaniard reached her first Slam final at the 2015 Wimbledon Championships, won her maiden Major in Paris in 2016 and backed it up with the Wimbledon title in 2017. Her exploits catapulted her to the pinnacle of the world rankings, truly establishing her as one of the biggest stars of women's tennis.
But then came a barren period. Muguruza failed to live up to expectations, succumbing to pressure in critical moments and sliding down the rankings. She rediscovered some of her best form last year as she reached the Australian Open final, but fell to Sofia Kenin in three sets.
But with her win at the WTA Finals in Guadalajara on Wednesday, the Spaniard not only managed to silence her detractors but also proved to herself that she is still very much a force to be reckoned with.
Speaking to the press after her straight-sets win over the in-form Anett Kontaveit in the final, Muguruza said she was delighted to show that she still belongs at the top of the women's game.
"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 28-year-old began the season strongly by winning the title in Dubai and registering runner-up finishes in Doha and the Yarra Valley Classic. After a mid-season slump, Muguruza found her rhythm once again in Chicago last month, going all the way.
At the WTA Finals in Guadalajara, the Spaniard lost her first match to Karolina Pliskova in a three-set thriller and then dropped the opening set of her second group match against French Open champion Barbora Krejcikova. Muguruza did not lose a single set thereafter.
The Spaniard saw off the challenge of Krejcikova and Kontaveit to qualify for the semifinals, where she overcame compatriot Paula Badosa in straight sets. She then defeated Kontaveit once again to lift the trophy in the Mexican city.
Reflecting on her performances this season, Muguruza went on to call it the "best year" of her career despite her failure to win a Grand Slam.
"Overall I think it's the best year for me," she said. "I might not have won a Grand Slam, but I deeply feel like I've been happier and more stable, less dramatic, and in general very happy about it.”
I have the tennis, I just have to show it: Garbine Muguruza on her recent struggles
The past few years have been hard for Muguruza. The Spaniard's confidence was shattered and she looked a pale shadow of the player who had lifted a couple of Slam trophies in the past.
Despite her struggles, Muguruza said she always believed she had the level to compete with the best and it was simply a matter of putting all the pieces together.
"The last couple of years, I didn't play the same way I played before," she said. "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 made finals of a Grand Slam, reached the rankings, I'm like, I have the tennis, I just have to show it," she added. It's hard, of course."
Muguruza, who was born in Caracas, also went on to reveal that she was extra motivated to qualify for the WTA Finals when she heard about the possibility of Guadalajara hosting the event.
“I was like, 'Oh, my God, I have to make it,' " she said. "And look now, we’re here.”
Following her triumph in Guadalajara, Garbine Muguruza will end the year as the world's third-ranked player.