Complex sentence: Rather than regional events, masters and teen athletes qualify for the games by a second online competition, following the Open--the top 200 athletes in each division worldwide are invited to compete in this qualifier, of which the top 20 advance to the Games.
Split into simpler sentences: Rather than regional events, masters and teen athletes qualify for the games by a second online competition, following the Open. The top 200 athletes in each division worldwide are invited to compete in this qualifier, of which the top 20 advance to the Games.