After a consistent season, Allen was back at the Crucible the following year where he beat Martin Gould in his opening match. He faced Ronnie O'Sullivan in the second round; confident and unaffected by his opponent's reputation, Allen beat the defending champion 13–11 for a quarter-final place in the 2009 World Championship. He then defeated Ryan Day by the same scoreline to reach the semi-finals, where he lost 13–17 to John Higgins, despite making a determined fightback from 3–13 down. Soon after his run in the World Championship, Allen won his first professional tournament, the 2009 Jiangsu Classic beating home favourite Ding Junhui 6–0 in the final.