Mastrovasilis took the silver medal in the under 18 division at the European Youth Chess Championships of 2000.

[1] In 2003 Mastrovasilis won the 1st Mediterranean Junior Championship in Ajelat, Libya.

[4] In 2007 he tied for 2nd–7th with Kiril Georgiev, Vadim Malakhatko, Mircea Pârligras, Hristos Banikas and Dmitry Svetushkin in the Acropolis International Chess Tournament.

In 2017 he was eliminated in 1st round by the Bulgarian GM Ivan Cheparinov losing 1.5 — 0.5 in their match.

[7] In 2023, he eliminated the Austrian GM Felix Blohberger in the tiebreaks and advanced to round 2, where he was eliminated by the Indian GM Vidit Gujrathi, also in the tiebreaks.