INDIAN WELLS, USA - Sachia Vickery has always been on the brink. The 22-year-old American has toiled away on the challenger circuit, battling to become a regular mainstay at the biggest tournaments on the WTA main tour. But every time she seemed a step - or even a point - away from a big leap forward, it just never went her way. 

Until Friday night. 

In front of a partisan crowd that never stopped backing her even after she fell behind by a set and 0-3 to World No.3 Garbiñe Muguruza, Vickery pulled off the biggest win of her career in one of the biggest tennis stadiums in the world at one of the biggest tournaments in the world, battling back to win 2-6, 7-5, 6-1 to advance to the third round of the BNP Paribas Open. 

Vickery's reaction after the win said it all. She was stunned. Her match against the reigning Wimbledon champion was just her third career-match against a Top 20 player. For the final hour of the match, Vickery could not put a foot wrong. She blasted winner after winner after the exasperated Spaniard, who couldn't believe her opponent's Midas touch. Then again, Vickery couldn't believe how good she was playing either.

"Honestly, probably when I wake up sometime tomorrow my coach will call me and say You just beat Muguruza. And I'll be like, No way.

"I didn't expect to win because I was down by so much. And to make that kind of turnaround on the world No. 3 player, you don't do that often. I think that's why I kept saying I was so surprised. I couldn't believe I won."

"I saw my mom [celebrating]. She's from Guyana and she loves always representing her country. I'm American and Guyanese also. She's always been supporting me since I started playing tennis and has been right there by my side. I was happy that I could win on such a big stage and most of my family is here. That was just unbelievable for me."

The signs have been there since the start of 2018 that this might be the breakout year for Vickery. She began the year by making the semifinals in Auckland as a qualifier, defeating Agnieszka Radwanska and defending champion Lauren Davis en route. As she readied for her qualifying campaign in Indian Wells last week, she finally made her Top 100 debut, coming in right at No.100 when the new rankings were released on March 5th. After a strong qualifying campaign, she saw she would have to go through one former Top 5 player in Eugenie Bouchard in the first round and a current Top 5 player in Muguruza in the second round.

"I started out pretty nervous," Vickery said after beating Muguruza. "Obviously, for me, I haven't played matches on such a big court before. For her, it's the norm.

"When I walked out on the court against Genie, I couldn't believe how big the court was. I have played on big courts, obviously, but nothing like this. I feel like that was really a hump to get over."

"Getting over the hump" was a phrase used often by Vickery to describe how much the win over Muguruza meant to her. A fantastic mover and gritty defender on court, Vickery has often found herself in winning positions only to falter in the past. One of her most notable let-downs came in the second round of the 2017 US Open, when she had two points match points against young Sofia Kenin to make her first third round at a Slam and earn a match against Maria Sharapova. Vickery botched both points and would go on to lose the last 10 points of the match, losing 6-4, 4-6, 7-6(0).

"I think actually me losing those matches where I have been up, I don't know, maybe 4-1 in the third set or 4-1 and 30-Love, that's actually helped me," Vickery said."Because now, even the past two matches, I have been up and I have kind of been reminding myself, you know, when I was up in those previous matches, even weeks ago, I was up 4-1 in the third set and didn't win another game. And I just keep telling myself, just hit the ball, go for it. Don't play tentative."

Backing herself and taking her chances have been the newest developments in Vickery's physical game. Against Muguruza, Vickery fired 26 winners - four more than the offensive-minded Spaniard - to 30 unforced errors. 

"My game for years has kind of been built around defense and not really taking on my shots," Vickery said. "And I think that was the thing I was happiest with in my first round and today."

"I think a lot of players that defend well, they can be aggressive. But I guess just after years and years of doing the same thing it's easy to get stuck in that kind of mentality, which was what happened to me.

"It's really taken a lot of work with my coach, you know, going after first serves and starting the point on the front foot so I'm not just running every single point. Obviously, as I play these better opponents, you know, you can't just run for two hours. You know, it's just not going to work out that way.

"I have honestly just put a lot of work in for the past few months, and I have made a lot of changes to my game. Everything is just kind of coming together. I have had so many matches in the past where I was just almost there, but I can never really just make that breakthrough. And I was just so close, just always losing it and losing it.

"Today I was just, like, go for it. Even if you lose, just lose hitting. That worked out really well for me."

"That was definitely Wakanda Forever," Vickery said when asked about her post-match salute to the crowd. "I'm so obsessed with the movie. It's taking over my life. I have seen it four times already. Literally, I'm obsessed. I have watched it twice here. I may just keep watching it because it's been working out well for me."

"Actually, the girl who plays Shuri, she's from Guyana, and that's where my mom is from. I was just like so crazy to see that and the movie is just so awesome. I'm just obsessed with it right now."

Vickery has had two turns on Stadium 1 and she'll get a third on Sunday night, when she takes on 20-year-old Naomi Osaka. Both women have been seed-slayers this week. Osaka has paved her own way to the third round with wins over Maria Sharapova and Radwanska. 

"I didn't even look at [the draw] to be honest," Vickery said. "I mean, who knew I would have beaten Muguruza. So I didn't even look past that point, to be honest.

"I'm just going to go in with the same mentality as I did today. I literally have nothing to lose. Everybody expected me to lose today. I just came out and surprised myself, and I surprised everyone."