313 at the beginning of the year in January, Molčan made his ATP debut at the 2021 Antalya Open in Turkey, where he defeated Andrey Golubev and Blaž Kavčič to qualify for the main draw.

[2] In February he won the doubles title at the 2021 Challenger La Manche with compatriot Lukáš Klein.

In March, he advanced through the qualifying rounds of Open 13 in Marseille, France, defeating Antoine Hoang and Ernests Gulbis to reach his second main draw appearance.

255 at the 2021 Belgrade Open, after qualifying yet again, Molčan reached the final of an ATP tournament for the first time in his career by defeating two Serbian wildcard players Hamad Međedović and Peđa Krstin, Spaniard Fernando Verdasco and clay specialist Argentinian Federico Delbonis which propelled him 74 spots up into the top 200 at World No.

[7] He overcame fellow qualifier and also making his debut Cem İlkel and Brandon Nakashima in five sets to reach the second and third round respectively for the first time in his career.

In November, he won the title at the 2021 Tali Open Challenger in Helsinki thus breaking into the top 100 at world No.

On his debut at the 2022 Australian Open he recorded his first win at this Major defeating lucky loser Roman Safiullin in the first round.

[15][16] He then advanced to his second career ATP final by defeating Botic van de Zandschulp[17] and Laslo Djere.

[20] Molčan hired fellow Slovak Marián Vajda to join his coaching team in May 2022.

[21][22][23] At the 2022 ATP Lyon Open he reached the third tour-level final of his career, and second of the season by defeating former World No.

[27] He made his debut at the 2022 Wimbledon Championships and won his first match at this Major defeating Pedro Martínez.

In Hamburg, Molčan reached the quarterfinals as an unseeded player, beating Marko Topo and 4th seed and defending champion Pablo Carreño Busta.

He advanced to the biggest semifinal of his career after Borna Ćorić retired during their match with Molčan leading in the second set.

[34] At the Australian Open, he earned his first win of the year by beating 2014 champion, Stan Wawrinka, in the first round in a five-set thriller.

[38] Seeded seventh at the Argentina Open, he fell in the first round to two-time champion Dominic Thiem.

Making his debut at this tournament, he defeated Albert Ramos Viñolas and upset 18th seed and world No.

[43] At the following tournament, the 2023 Miami Open, he reached in two weeks back-to-back third rounds of a Masters 1000, defeating Jordan Thompson and upset 28th seed Yoshihito Nishioka.