[2] In August 2018 he played in a professional ranking tournament for the first time, and beat Adam Stefanow in the first round of the 2018 Paul Hunter Classic.

[3] In January 2019, he defeated Michael White, then ranked #36 in the world, at a snooker tournament in Bruges.

[4] At the 2019 Snooker Shoot-Out, a ranking tournament for which he got a wild card, he beat James Wattana in the first round.

[5] In March 2020 he lost in the semi-finals of the EBSA European Under-21 Snooker Championships to later champion Aaron Hill.

This record was broken by Liam Davies, who was two days younger than Mertens when he won his first match at the 2022 World Snooker Championship qualifiers.