Humphries took a 2-0 lead and looked strong, but Wattimena stormed the next five sets to pull away at 5-2.
'Cool Hand Luke' was able to claw back a set, but his opponent finished the job to record an eye-catching 6-2 triumph in the round of 16.
Earlier, Stephen Bunting beat Dutch starlet Gian van Veen 6-5 at Maaspoort Den Bosch.
The duo traded sets, until Bunting - who began with the darts - extended his lead from 3-2 to 5-2 as he threatened to pull away.
But Van Veen stood firm and brought the match all the way back to 5-5 before 'The Bullet' finished the job at 6-5.
Following Bunting's win, Welsh star Gerwyn Price was able to beat Danny Noppert in what was a tighter match-up than the score may suggest.
They traded legs before 'The Iceman' edged ahead at 3-2 to ultimately win at 6-2.
Home favourite Michael van Gerwen then made barely any mistakes in a 6-1 victory over compatriot Dirk van Duijvenbode.
Earlier, Nathan Aspinall was stunned by Kevin Doets. 'The Asp' was only able to claw back one set as Doets romped to a 6-1 win.
Englishman Rob Cross was able to overcome Richard Veenstra to the tune of 6-3, however.
In the final match of the evening, Luke Littler beat Belgian Dimitri van den Bergh 6-4 to book his place in the quarter-finals - where he will face Van Gerwen.