Klaasen overcame Joe Cullen and Mervyn King to advance to the third round of the World Championship for the first time since 2009. He missed one dart at double 18 to complete a 147 finish and defeat Phil Taylor 4–2, before going 2–0 down in legs in the final set. Taylor missed one dart to win the match and Klaasen took full advantage by winning four legs on the trot, wrapping it up with an 11 darter. In the quarter-finals, Klaasen was 3–1 and 4–3 behind Alan Norris in a race to five. He was two legs to one down in the next set but produced back-to-back 11 dart legs to win it and then clinched the final set without conceding a leg to advance to the semi-finals of a PDC World Championship for the first time, where he faced reigning champion Gary Anderson. Klaasen's victory also marked the first time that a player has won their next game after knocking Taylor out of a PDC World Championship. In the semis he was thrashed 6–0 by Anderson, who averaged 107. Klaasen also reached the semi-finals of the next major event as he whitewashed Kyle Anderson 10–0 at the UK Open, but he lost 10–5 to Peter Wright. He was defeated 10–6 by Steve Beaton in the opening round of the World Matchplay and at the same stage of the World Grand Prix, 2–1 in sets by Adrian Lewis.