Klaasen reached the second round of the 2012 World Championship with a 3–1 win over Peter Wright, but was beaten 0–4 by James Wade in the second round. His best result of 2012 was in reaching the quarter-finals of the third UK Open Qualifier in March where he lost 4–6 to Mark Jones. At the UK Open itself he was defeated in the last 64 by Raymond van Barneveld 3–9. After revelations emerged with regard to Klaasen's personal life detailed below he did not play again in the rest of 2012, which included missing the 2013 World Championship.