STUTTGART, Germany -- Elise Mertens has her work cut out for her as she prepares for her first career meeting against World No.1 Iga Swiatek. The 28-year-old Belgian secured a three-set win over Tatjana Maria in the first round of the Porsche Tennis Grand Prix on Tuesday to set up the first-time clash with Swiatek on Thursday in Stuttgart. 

"At the age of 22, it's unbelievable what she's already achieved," Mertens told reporters. "Definitely in the future, too, she will achieve a lot more."

The match will be Mertens' third against a No.1 and first in nearly four years. She holds 11 Top 10 wins in her career but is 0-2 against a reigning No.1. Both losses came to Simona Halep on clay in 2018. 

Mertens reached a career-high No.12 in 2019 and comes into Stuttgart ranked No.30. She began the season with a run to the final in Hobart, but after a slight dip, Mertens says she's stabilized her game in the last month. She notched a resounding straight-sets win over Naomi Osaka at Indian Wells before posting the best win of her year, by ranking, over Elina Svitolina in Miami. 

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Her momentum has been stalled by tough draws. She ran into No.3 Coco Gauff in the California desert and a red-hot Danielle Collins in Miami. 

"Of course I can always do things better, I can always work on things," Mertens said. "But I feel like I'm pretty steady at the moment. Having some tough draws, of course, in the past, but I can only learn from these matches. 

"I'm 28, so I'm not the younger ones, but I still feel like tennis gives me a lot and I have a lot of passion for tennis. I always try to improve, and I think that's my work ethic, just try to improve every time. I think that's why I'm still there in the ranking."

After being a Top 20 stalwart for nearly four seasons from 2018 to 2022, Mertens credits her experience and maturity for her general sense of calm as she plots her way back up to where she belongs. 

"I felt like when I was 20 years old, I felt like I need to win this one, I need to win this, I need to win this match," Mertens said, "because if I lose, two losses in a row, something like that, [I was] just panicking a bit more. I feel like now, OK, I lost the second set, but I can do it again. This is a new set, new match.

"I think it's more relaxed. Sometimes I'm a bit stressy, too, of course. I think it's more, like, OK, trust yourself a bit more, what I can do as a tennis player."

Player Highlights: Elise Mertens

Mertens has faced Swiatek before, but that came on the doubles court in 2021. She'll spend her off day reviewing tape to devise a game plan, but Mertens is well aware of the challenge of unseating the reigning two-time champion. 

"[What stands out to me is] the mental toughness, I think, and not giving any points away, taking the ball on the rise, taking it early," she said. "And her footwork of course, too.

"She's a bit like an all-court, all-around player, so you don't really find a lot of weaknesses. I think of course that's why she's No.1."

Mertens has the ability to surprise. While her gritty defending and counter-punching has been the hallmark of her career, she has the tools and mindset to be aggressive when she needs to. She left Osaka shell-shocked when she overpowered the four-time major champion in a 7-4, 6-4 win last month. 

"I definitely wanted to be the aggressive one," Osaka said after that loss. "I felt like in some ways I was kind of on defense a lot, and I wasn't able to hit the ball as like heavy as I usually feel like I should.

"And then in the ways that she surprised me, I think her service speed probably went up since I last played her."

That victory over one of the tour's premier power players will give Mertens confidence as she eyes the upset. 

"I think I just have to dominate a little bit, go into the court, not hesitate at all, because she will get that ball back," Mertens said. "She will hit the ball. Of course she has a lot of experience on these courts already, winning it twice.

"Yeah, let's see what I can do against her. In tennis, you never know."