The world No. 1 held off Aspinall in a high-octane first round. The Asp lit up the Mattioli Arena with a 170 checkout, but Humphries pinched the opening set and replied with a superb 156 on the way to a 2-0 victory.
"It was a big game tonight," Humphries said. "Nathan is a fantastic player, but he let me in a couple of times, and that 156 was massive for me. My starting doubles were good. My scoring wasn’t as strong, but hopefully I can come back on Wednesday and be better."
Joe Cullen returned to form on TV by dispatching two-time champion Wade 2-0, landing six doubles from 11 attempts. Cameron Menzies upset No. 8 seed Dobey by the same score for his first win on the World Grand Prix stage.
Krzysztof Ratajski raced through with a dominant triumph over German No. 1 Martin Schindler, dropping just one leg for a 95.94 average. His reward is a second-round tie with Humphries.
Rob Cross survived a scare in the evening’s opener, edging debutant Wessel Nijman after the Dutchman missed a match dart at the bull. Cross was tidier on the outer ring, nailing eight of 16 at double, and will meet Menzies.
Elsewhere, Danny Noppert saw off Jermaine Wattimena by the same score, sealing it with a 158 finish that briefly lifted the roof.
Gary Anderson came through a last-leg decider against Raymond van Barneveld after the Dutchman dragged their tie into a third set. The Scot finished strongly to book a round-two meeting with Cullen.
Stephen Bunting produced the night’s standout display, averaging 97 with five 180s and 116 and 130 checkouts in a straight-sets win over Niko Springer. He faces Noppert next.
The first round concludes on Tuesday, when Mike De Decker begins his title defence against two-time world champion Peter Wright. Luke Littler faces Gian van Veen in the pick of the ties, while Michael van Gerwen opens his pursuit of a seventh double-start crown against Dirk van Duijvenbode.
Former champions Gerwyn Price, Jonny Clayton and Daryl Gurney also begin their campaigns against Ryan Searle, Andrew Gilding and Ross Smith, respectively.
Monday's results
Rob Cross 2-1 Wessel Nijman
Krzysztof Ratajski 2-0 Martin Schindler
Cameron Menzies 2-0 Chris Dobey
Joe Cullen 2-0 James Wade
Danny Noppert 2-1 Jermaine Wattimena
Luke Humphries 2-0 Nathan Aspinall
Gary Anderson 2-1 Raymond van Barneveld
Stephen Bunting 2-0 Niko Springer
Tuesday's fixtures
Damon Heta v Luke Woodhouse
Ross Smith v Daryl Gurney
Jonny Clayton v Andrew Gilding
Gerwyn Price v Ryan Searle
Luke Littler v Gian van Veen
Michael van Gerwen v Dirk van Duijvenbode
Peter Wright v Mike De Decker
Josh Rock v Ryan Joyce