In the 2009 UK Championship he led Graeme Dott 6–2, before Dott retired due to illness and Williams thus won the match 9–2. After this he lost his next match against Peter Lines 8–9. At the Masters he won his wild card round match, beating Rory McLeod 6–2. Then he won his first round match against Ali Carter 6–3 to progress to the quarter-finals of the event, despite being involved in a traffic accident the day before his match against Carter. It was reported that a car drove into the back of the 4×4 that his sponsors had lent him, which was carrying Williams and Hendry to a restaurant. In the quarter-finals he defeated Shaun Murphy 6–4, but eventually lost a high-quality match in the semi-finals 5–6 against Ronnie O'Sullivan. In the Welsh Open, he reached the quarter-finals, beating Fergal O'Brien 5–2 and Andrew Higginson 5–0, before losing against Stephen Maguire 1–5.