After new rules for qualification for UK Open, Dekker was seeded into the third round of 2019 UK Open. He won over Harry Ward (darts player), but lost in the fourth round to Simon Whitlock. This was the only major he participated in this season. His only two good results in the season were two quarterfinals in PDPA Players Championship 8 and 20. At the end of the year, he dropped to 56th place in PDC Order of Merit after not being able to defend his prize money from 2017 Players Championship Finals. His Tour card was secured only because he won West European Qualifier for 2020 PDC World Darts Championship.