CHARLESTON, SC, USA -- No.1 seed and former champion Sloane Stephens of the United States moved into the third round of the Volvo Car Open on Tuesday with a grinding 7-6(4), 7-6(4) victory over Sara Sorribes Tormo of Spain.

"It was a tough day, and I was just happy to get through," Stephens said, during her post-match press conference. "Obviously a lot of different factors, but just happy with the fight and happy that I was able to get through."

The top-ranked American in the WTA rankings prevented World No.78 Sorribes Tormo from obtaining her first Top 10 win of her career, as Stephens came back from set point down in the opening set to clinch the hard-fought, two-tiebreak-set victory after a grueling two hours and 37 minutes of classic clay-court play.

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"[Sorribes Tormo] doesn't play like most of the girls play," said Stephens. "She hits a lot of slices. She runs around a lot, stays around the baseline. Just plays kind of a different game style than most. She hits a lot of moonballs. She just has a lot of different variations, so it's tricky to play against her."

"All in all the court was playing a little bit slow because it rained last night," the top seed continued. "It was a little sticky, and like I said, a lot of different factors, but I was happy to get through."

Stephens had 37 winners and 55 unforced errors in the match, while Sorribes Tormo had 20 winners compared to 29 unforced errors. Each player broke serve six times, but Sorribes Tormo went 6-for-9 on break points while Stephens let 11 of her 17 break chances go begging. Nevertheless, Stephens won nearly 60 percent of points on the Spaniard's second serve to help her eke out a win.

World No.8 Stephens has now won six straight matches in Charleston, despite missing the event in 2017 and 2018. The American took the 2016 championship in her most recent appearance at the tournament, defeating Elena Vesnina in the final.

Stephens will meet either No.14 seed Ajla Tomljanovic of Australia or Slovenia’s Tamara Zidansek in the third round.

The match started with Sorribes Tormo in control, breaking an error-prone Stephens in the first game. The Spaniard used her heavy forehands to maintain her lead, holding through to 4-2 against the increasingly frustrated Stephens. In that game, Sorribes Tormo reached break point with a passing winner, then broke for 5-2 with a service return smack on the sideline.

But after a coaching timeout on that changeover, Stephens returned to the court with a rejuvenated purpose. The American cut down on her unforced errors and amped up her forehand, earning a love break for 5-3. Stephens then faced a set point in her next service game, but steeled herself to hold for 5-4.

Sorribes Tormo began to falter, and dropped serve for the second straight time, leveling the set at 5-5. The Spaniard then had two set points against her at 6-5, but Stephens missed forehands on those chances, and Sorribes Tormo held on to set up a tiebreak.

Stephens double faulted to open the tiebreak, but then started a tear with her forehand, reeling off a winning streak to get to 5-1. Sorribes briefly pulled back to 5-4, but a forehand winner down the line gave Stephens a third set point. There, Stephens put a backhand winner deep into the court to claim the hard-earned, 67-minute opening set.

Stephens looked like she might cruise through the second set, breaking the Spaniard at love in the opening game. But Sorribes Tormo refused to yield, and broke back for 1-1 after Stephens squandered game point. The two players then engaged in a 15-minute game, where the American broke again for 2-1 on her seventh break point of the game.

But Stephens was unable to hold a lead, as she squandered two game points and allowed Sorribes Tormo to break her for 3-3. The American broke Sorribes Tormo in each of her next two service games as well, but the Spaniard was able to re-break each time, including at 5-4, when Sorribes Tormo’s solid forehand helped her erase two match points.

Another tiebreak started, with Stephens falling behind 4-2 after the spin on Sorribes Tormo’s shots forced the top seed into errors. But a strong Stephens forehand pulled her back level at 4-4, and poorly-timed errors by the Spaniard suddenly gave Stephens a 6-4 lead and a third match point. There, the Spaniard netted a service return to hand Stephens a fifth straight point and the win.