LUGANO, Switzerland - No.2 seed Elise Mertens needed to do some heavy lifting to reach her second WTA final of the season on Saturday, as the World No.20 won not one, but two three-set matches to advance to the championship.

Mertens started her afternoon with a two hour, 36-minute battle against Germany's Mona Barthel in the quarterfinals, as she came from a break down in the final set to win 6-4, 5-7, 7-6(0), before later dispatching Belarusian qualifier Vera Lapko in the semifinals, 6-1, 4-6, 6-4 in just over two hours.

The Hobart International champion prior to the start of the Australian Open in January, Mertens will face Lapko's compatriot, Aryna Sabalenka, in the final after the Belarusian won two straight-set matches on Saturday with the loss of just nine games.

Read more: Sabalenka vanquishes Voegele in Lugano to reach final 

“It’s mentally tough [playing two singles matches in one day] and also for the body, which sometimes didn’t want to move that well today!" a weary, but elated Mertens said after the match against Lapko.

"I pulled through against a really good player. She’s still young and a hard-hitter, so I had to stay aggressive. I’m happy with my performance today - and I still have to play a doubles match later!"

Mertens also trailed by a break in the final set against Lapko, as the qualifier was looking to win her sixth match this week to advance to her first WTA final, but the Belgian won the last three games to squeak out another victory.

Mertens' marathon effort was the result of a week of rain in Lugano, which ensured that the No.2 seed did not finish her second round match against Marketa Vondrousova until Friday.

Read more: Mertens survives Vondrousova as rain continues in Lugano

“The first couple of days this week, we didn’t really practice, so I went to the gym and did some things to keep myself warm for when I needed to go on court," the Belgian said of the weather. "I think it’s just about mentally staying tough in every moment.

“I take it match by match. Whether it’s the first round or the final, you just want to win the match. If the level is good and you play your game, then maybe something can happen."

Mertens' marathon Saturday continued later in the afternoon, as she and compatriot Kirsten Flipkens partnered in the doubles semifinals to defeat Kristyna Pliskova and Galina Voskoboeva, 6-3, 7-5.