Christopher O'Connell vs Darian King • Belgrade 2021
QQualifier — came through qualifying
WCWild Card — invited by the organizers
LLLucky Loser — lost in qualifying, entered after a withdrawal
PRProtected Ranking — ranking protected during a long injury
SESpecial Exempt — still playing another event, skips qualifying
JEJunior Exempt — place earned by a top junior ranking
COOrganiser's Choice — courtesy, coach or committee place
NGNext Gen — place for a young player (ATP)
JRJunior Reserved — ITF place reserved for top juniors
SRSpecial Ranking — WTA protected ranking (injury or maternity)
ALTAlternate — entered after a withdrawal, not from qualifying
BYEBye — goes straight to the next round
