Ivan Barbashev and Samuel Blais each scored in regulation to put Group B ahead 2-0, but Group A rallied back with goals from Tage Thompson and Brayden Schenn to force overtime.
Blais and Barbashev each scored again in the shootout before Paul Stastny buried the deciding goal - a top-shelf backhander - to secure a 3-2 win for Group B in a seven-round shootout.
"I don't want to take anything away from our veterans, because we had some (of those) guys look good out there," Blues Head Coach Mike Yeo said after the scrimmage. "But this is typically what you see. The young kids come in and they've got a lot of energy, and as camp goes on, the level of play continues to go up. The story is going to be who can continue to move up, continue to improve as camp is moving along. Some guys have shown a lot of good things so far."