Thornton was the only player to reach the quarter-finals of the 2015 World Championship without dropping a set. In his first appearance in the last eight of the event trailed Michael van Gerwen 3–0 in sets, before winning two unanswered sets. Thornton missed one dart to level the game at 3–3 and was ultimately defeated 5–3. His average of 101.49 was the first time he has been over the 100 mark in a World Championship match.