Day lost in qualifying for the opening ranking event of the 2012–13 season the Wuxi Classic 0–5 to Robert Milkins.&lt;ref name="2012/13"&gt;&lt;/ref&gt; He was then beaten in the second round of the Australian Goldfields Open and the Shanghai Masters, 3–5 to Matthew Selt and 0–5 to John Higgins respectively. Day was defeated 3–6 by Neil Robertson in the opening round of the International Championship, but then came perhaps the best result of his season at the UK Championship. He beat Ding Junhui 6–4 in a high quality first round encounter, before letting a 3–0 lead against world number two Mark Selby slip to lose 4–6. Day played in nine of the ten minor-ranking Players Tour Championship events during the season with his best results being two quarter-final defeats to be ranked 32nd on the Order of Merit, just outside the top 26 who qualified for the Finals. Day struggled in the second half of the season as he failed to qualify for four of the remaining five ranking events, losing 2–5 in the first round of the World Open to Mark Allen in the one he did reach. He failed to qualify for the World Championship for the first time since 2006, narrowly losing to Ben Woollaston 9–10 in the fourth and final qualifying round. He finished the season ranked world number 31.