CHARLESTON, SC, USA - Top seed and 2016 champion Sloane Stephens pulled off an audacious comeback under the lights at the Volvo Car Open, rallying from the brink of defeat to knock out Ajla Tomljanovic, 4-6, 6-4, 6-4 to reach the quarterfinals.

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"I was just thinking, fight!" she explained in her post-match press conference. "I haven't had the best start to the season, and sometimes you gotta just like gut it out."

The 2017 US Open winner initially trailed Tomljanovic by a set and two breaks as the Aussie looked for a second Top 10 win in two weeks. The American ultimately turned the tables to secure the win after two hours on Volvo Car Stadium.

"Ajla played really well today; I think she played at a really high level, and it made me raise my level. For the first time in a long time I really was like, 'I gotta beat this girl.' Like I wanted to be out there, and I was really fighting, and I didn't care what it took."

Tomljanovic enjoyed a breakthrough win over Aryna Sabalenka last week at the Miami Open and, although she'd never beaten Stephens in four previous meetings, appeared in-form early against the former World No.3, taking the only break of the opening set to move within reach of the upset.

"I thought she was playing really well and she wasn't missing a lot. She obviously was ripping through the ball, so that's tough when you're playing someone like that because you don't really get a great rhythm."

Feeling the momentum early in the second set, Tomljanovic won 11 straight points to earn a 3-0 lead. Just as defeat seemed certain, Stephens clicked into gear, winning five games in a row to find herself serving to level the match, forcing a decider with one last break of serve.

"Once I started hitting and getting into it more, I kind of got a better rhythm. So I was like, 'Okay, she's going to hit; I have to hit.' So once I think I started doing that, I just kind of settled down a little bit and stayed calm. I didn't panic. I think in the last couple of matches I've been playing, I normally don't panic, but I was just like really uneasy. But today, I was like, 'Just wait it out, it'll be okay, bounce up and down a little bit, and Jesus, take the wheel.'"

The final set went largely with serve as the two looked for opportunities to break. Again, Tomljanovic broke first and held a point for 5-3 only for the former French Open finalist to turn the tables once more, winning the final three games of the match to reach her first WTA quarterfinal of 2019.

In all, Stephens struck 22 winners to 26 unforced errors, and converted six of 15 break point opportunities; while Tomljanovic struck more winners, she also made more unforced errors - particularly in the final game as she hit three off the forehand to bring up match point - finishing with 30 to 38, respectively.

Up next for the American is a rematch of last spring's Roland Garros semifinal against Madison Keys, who defeated 2017 Volvo Car Open runner-up Jelena Ostapenko earlier in the day.

"We practice together a lot. We've only played three times. But I honestly, I couldn't even tell you. I just go out and try to play my game and execute a game plan, and it's worked so far. So I don't have any like magic secret stuff, and if I did, I wouldn't tell you because then, obviously, that's printed!"