Robertson qualified for one ranking event in the 2011–12 season, the World Open, thanks to wins over Andrew Norman, Ken Doherty and Rory McLeod, before seeing off amateur Zhou Yuelong in the wildcard round at the event in Haikou, China. In the first round of the event proper he played Mark Allen and was beaten 1–5, with the Northern Irishman later going on to win the tournament. Robertson reached the semi-finals of Event 7 of the minor-ranking Players Tour Championship series, where he lost 0–4 to Matthew Stevens. He played in 11 out of 12 of these events, also picking up a last 16 finish in Event 4 to be placed 31st on the PTC Order of Merit, just outside the top 24 who made the Finals. Robertson finished the season ranked world number 55, inside the top 64 who automatically retained their places for the 2012–13 season.