Nicholson came 5-2 up, but missed matchdarts in three of the next four legs. Van de Pas levelled the match at 5-5 in the tenth leg, before stealing the victory with a 17-dart leg.
Daryl Gurney had not many troubles with Rene Eidams, as he dropped only one leg against the German.
Mervyn King edged out James Wade 6-3.
2018 German Darts Open
Saturday April 14 Second Round
Afternoon Session (1pm local time, 12pm GMT) Darren Webster (103.38) 6-2 (101.19) Steve West
Ian White (83.67) 6-3 (84.25) Cameron Menzies
Gerwyn Price (93.75) 6-4 (87.39) Kirk Shepherd
Jelle Klaasen (83.56) 6-1 (78.54) Maik Kuivenhoven
Steve Beaton (89.55) 2-6 (94.13) Alan Tabern
Dave Chisnall (108.65) 6-0 (89.54) Jose Justicia
Michael Smith (95.69) 6-4 (92.77) Steve Lennon
NB: Simon Whitlock's
withdrawal through illness means that Daniel Larsson receives a Bye.
Evening Session (7.15pm local time, 6.15pm GMT) Mervyn King (94.20) 6-3 (95.03) James Wade
Daryl Gurney (92.68) 6-1 (81.72) Rene Eidams
Benito van de Pas (85.98) 6-5 (86.48) Paul Nicholson
Michael van Gerwen v Danny Noppert
Peter Wright v Max Hopp
Joe Cullen v Luke Humphries
Mensur Suljovic v Jermaine Wattimena
Rob Cross v Dimitri Van den Bergh