But Walkersville scored the last 10 points - including six by Greg Mason - of the first quarter to go in front, 18-14.
The Lions left the Warriors behind with a 16-5 run over the final five minutes of the first half to take a 40-28 halftime lead. McCollum scored 10 of the Lions' final 16 points of the first half.
McCollum picked up where he left off, getting six points in an 8-0 run in the first minute of the third quarter to increase the Lions' advantage to 48-28.
"We came out slowly in the first quarter," Walkersville coach Bruce Zimmerman said. "But then we really picked up the pace during the second and the third quarters. If we want to be a good team, we have got to be ready to play at the beginning of the first quarter."
Luther Weedon scored 14 points and Dave Berry had six assists for Walkersville (3-1). Chris Hannigan had nine rebounds and Mason had seven.
Brad Wetzel had 20 points and seven rebounds, Seligman had 11 points and Corey Shea had four assists for the Warriors (1-3).
"I am proud of my kids for not giving up," Boonsboro coach Sam Connelly said. "These kids work hard in practice every night. I never have to yell at anybody for being late or lazy."