Day finally clinched his maiden ranking title in his fifth final appearance. The Welshman defeated Stephen Maguire 5–2 to claim the Riga Masters title. The Welshman sensationally stormed to consecutive titles at the 2018 Gibraltar Open and the 2018 Romanian Masters. He defeated Cao Yupeng and Stuart Bingham in the respective finals. Day reached the semi-final in the UK Championship, this was his first appearance in the semi-finals of a Triple Crown event, but he lost 6–3 to Shaun Murphy in the semi-final. Day also made a return to the Masters for the first time since 2010. He beat Ding Junhui 6–4 in the first round, but lost to John Higgins 6–1 in the quarter final.