Aussie John Millman made a superb start to the final ATP regular season event in Bulgaria with a 6-3 6-1 victory against local wildcard Adrian Andreev.
The Sofia event was scheduled for the end of September but was delayed due to the COVID-19 pandemic.
Millman will face either Slovak Andrej Martin and French qualifier Gilles Simon in the second round of the tournament that has seen a number of withdrawals.
Canadian Denis Shapovalov will be the star attraction and the top seed and will be joined by Felix Auger-Aliassime.
Alex De Minaur is No. 3, Jan-Lennard Struff No. 4 followed by Adrian Mannarino, Millman, Nikolaz Basilashvili and Marin Cilic.
Shapovalov will open against Radu Albot and could meet Mannarino in the quarters and De Minaur in the semifinals.
Auger-Aliassime could get Cilic in his quarter then potentially Struff in the semis.
Italian Jannik Sinner and Gilles Simon are also in the draw.
Milos Raonic, Kei Nishikori, Kevin Anderson, Pablo Carreno Busta, Diego Schwartzman and Borna Coric were among the withdrawals from the event.