NEW YORK, NY, USA -- No.15 seed Elise Mertens of Belgium claimed a hard-fought third-round victory in the 2018 US Open on Friday, getting past No.23 seed Barbora Strycova of the Czech Republic, 6-3, 7-6(4), and reaching the fourth round of the US Open for the first time in her career.

In the first meeting between Mertens and Strycova, the Belgian needed to save three set points at 6-5 in the second set in order to prevent the match from going to a decider, ultimately prevailing in two sets after just over two hours of play.

"[Strycova] played a great game today," Mertens told the media, after the match. "I think I stepped up in the first set, a little more aggressive. Of course, she comes to the net a lot. But, not a lot of mistakes; in the rallies, if it came back shorter, I tried to make the point."

2018 Australian Open semifinalist Mertens, the first Belgian to reach the third round of the US Open since 2010, moved through the tight match with two more winners and two fewer unforced errors than Strycova. The top-ranked Belgian on the WTA also claimed over two-thirds of points on Strycova's second serve.

In the fourth round, Mertens will face defending champion Sloane Stephens of the United States, who ousted two-time US Open finalist Victoria Azarenka of Belarus in straight sets on Friday. Mertens won their only prior meeting in straight sets, in Cincinnati two weeks ago.

"Well, you know, she’s a great player," Mertens said of Stephens. "She won the tournament last year, so it’s going to be a tough match. I’ve played her once, and it was a really tough match, so I hope it’s going to be exciting."

"Of course [Stephens] has experience with the big stages, but I’ve got nothing to lose," Mertens continued. "I’m playing a good game, and I’m feeling confident, feeling ready to play."

Two extremely long games at the outset featured both players muddling through on serve to reach 2-1, as it became a battle between Strycova’s forward motion and volleying prowess, and the pinpoint groundstrokes and passes of Mertens. And, indeed, it was Mertens who struck first, breaking for 3-1 after Strycova pushed a backhand volley into the net on break point.

However, at 4-2, the Czech regrouped to get back on serve, striking a solid return on break point and forcing a netted forehand from Mertens. But the Belgian immediately retained that break advantage in the next game, using her effective forehand to maneuver to break point, at which point Strycova double faulted to hand over the game.

Serving for the set at 5-3, Mertens blasted a forehand winner behind Strycova to reach set point, which she converted when a powerful backhand by the Belgian perfectly set up a point- and set-winning backhand volley.

Mertens claimed a quick lead in the second set as well, breaking an error-prone Strycova for a 2-1 lead, and then holding at love for 3-1, giving the impression that it would be a quick day at the office for the Belgian.

But Strycova continued to charge towards the net whenever she could, and her aggressive play finally allowed her to strike back, breaking Mertens to level the set at 4-4. Strycova then proved her mettle by coming back from triple break point down to hold for 5-4, sealing the comeback within the game with an ace.

Later, serving at 5-6, it was Mertens who had to struggle, as her groundstroke errors gave Strycova three break points in the game, which doubled as set points. But Mertens persevered through a five-deuce game by rediscovering the consistency on her shots, and the combatants headed into a second-set tiebreak.

The players were deadlocked at 3-3 in the tiebreak until Mertens unlocked her backhand brilliance, knocking off two big shots off that win in a row to take the 5-3 lead. At 5-4, a long miscue by Strycova gave Mertens double match point, and the Belgian converted the first after Strycova fired a final forehand into the net.