In 2007, Mardle was beaten in the opening round of the World Championship by unseeded Alan Caves, and subsequently failed to reach the latter stages of a single event that year. He found his form at the 2008 World Championship, and in a big upset he beat then-13 time champion Phil Taylor 5–4 in the quarter-finals, a match in which he had trailed 3–0. This was the first time in the history of the PDC championship that Taylor had been beaten before the final. After his win over Taylor, Mardle was made bookmakers' favourite to win the tournament, especially as his semi-final opponent was 21-year-old qualifier Kirk Shepherd, ranked 142nd. However, an over-confident Mardle lost the match 6–4. Mardle later described his attitude going into the match as "nonchalant" and stated that he did not give Shepherd the respect he deserved.