At the outset of the 2010–11 NHL season, Reimer again was assigned to the AHL's Marlies. He was not expected to contribute to the Maple Leafs at the NHL level during the 2010–11 season. Expectations for the young netminder were low heading into the season, with head coach Ron Wilson saying, "We wanted him to play in the minors and continue to get better, develop and try to stay healthy." He was recalled by the Maple Leafs several months into the season, making his NHL debut on December 20, 2010, in relief of Jonas Gustavsson against the Atlanta Thrashers. He played 14 minutes in the third period, stopping all four shots he faced. Reimer made his first NHL start against the Ottawa Senators on January 1, 2011. The Maple Leafs won the game 5–1, with Reimer recording 32 saves while picking up his first career NHL win. On February 3, 2011, Reimer recorded 27 saves and picked up his first career NHL shutout against the Carolina Hurricanes. A combination of injuries and poor play by Gustavsson and Jean-Sébastien Giguère provided an opportunity for Reimer at the NHL level. His strong play caused the Leafs to carry three goalies on their NHL roster, a fact which did not surprise Giguère, who said, "The way he played the last time he was up, you knew he was going to get another chance." Ron Wilson acknowledged Reimer as the team's starting goaltender as they set out on a late-season run for a playoff spot, saying, "It's going to be his ball the rest of the way. As long as we stay in the race. And I think he's up to it."