As NHL play resumed the following season in 2005–06, Wellwood joined Toronto's lineup. When captain Mats Sundin was injured in the first game of the season, Wellwood was bumped to centre the first line between wingers Alexei Ponikarovsky and Nik Antropov in Sundin's absence for a month. Wellwood posted a career-high 45 points in his rookie campaign, and in the following season, on December 16, 2006, Wellwood scored his first career NHL hat-trick in a game against the New York Rangers, also posting two assists for a career-high five-point NHL game. On pace to surpass his rookie totals, Wellwood was sidelined for almost half the season and finished with 42 points in 48 games.