Humphries, reigning world champion and match play champion, showcased his elite levels which have contributed to his stellar 2024 so far and extending his winning run at the World Grand Prix to seven matches.
Despite a slow start against Pietreczko, Cool Hand Luke recovered to dominate the match, finishing with a clinical 90 checkout.
"Ricardo played a fantastic game of darts," Humphries acknowledged to the PDC website. "If he played anybody else tonight he might have won the game, but I managed to scrape through in the end.
"Those six darts at the end of the third set were crucial. It could have been a lot different, but that 180 followed by the 130 won me that game."
Humphries will now face 2021 champion Jonny Clayton, who defeated Ross Smith 3-1.
Clayton praised his own resilience, saying: "You have to find something, but it's really difficult when you're playing against a good friend like Ross."
Other notable results included Rob Cross's victory over Martin Schindler and Ryan Joyce's dramatic sudden-death win against Nathan Aspinall.
The BoyleSports World Grand Prix continues on Thursday with matches featuring former champions Gerwyn Price, James Wade, Daryl Gurney, and Joe Cullen.
Thursday schedule:
Gary Anderson v Mike De Decker
Gerwyn Price v James Wade
Daryl Gurney v Joe Cullen
Dave Chisnall v Dimitri Van den Bergh
