In October 2011, he made his debut in the doubles event of an ATP Challenger Tour tournament, at the 2011 Open de Rennes.

In July 2015, Lamasine reached his first career ATP Challenger Tour singles final at the tournament in Tampere.

It was his first career singles match in the main draw of an ATP World Tour or Grand Slam tournament.

That was his first career singles match in the main draw of a non-Grand Slam ATP World Tour tournament.

He went on to register his first career singles win in the main draw of an ATP World Tour tournament by defeating Radu Albot in straight sets in the first round.

[2] At the Lyon Open, Lamasine gained entry to the singles main draw as a lucky loser when Mikhail Kukushkin withdrew due to right shoulder pain.