He hit a rare home run in the first American League Championship Series game ever played in 1969, and after uncharacteristically hitting .333 in the 1970 ALCS, his contributions led to the Orioles' 1970 World Series victory, the team's second title in five years. During the series, he caught a line drive to end a 4–3 victory in Game 1 with the tying run on first base, and he had an assist to end Game 3. Belanger played in six ALCS series and set league playoff records for career games, putouts, assists, total chances, and double plays by a shortstop. (All these records were broken between 1998 and 2002 by Omar Vizquel and Derek Jeter.)