Before playing with Boston, he played a season with their AHL affiliate Providence Bruins. He was called up and played in his first NHL game on January 30, 2007. The game ended in a 7-1 loss against the Buffalo Sabres and Krejčí suffered a concussion from Buffalo right winger Adam Mair. He scored his first hat-trick in a 8–5 Bruins win against the Toronto Maple Leafs. He won the Stanley Cup with the Bruins on June 15, 2011 when they defeated the Vancouver Canucks 4-0 in Game 7.