Reigning champion Humphries upset at Grand Slam of Darts, Littler starts with win
Rodriguez shocked the world number one late on in Wolverhampton, recording a 141 checkout to seal a stunning 5-3 victory.
Humphries had fought to keep himself afloat in the penultimate leg but it proved meaningless as Rodriguez showcased a ruthlessness.
It was a different feeling for Luke Littler, who fired a 112.16 average to beat Keane Barry 5-0.
The teenager looked in a buoyant mood which was highlighted by a wonderful 121 checkout which sent him on his way in a match lasting just six minutes and 48 seconds.
"I've been practising very well leading up to the Grand Slam, and I'm glad I played so well on my debut tonight," Littler said.
"I felt good. It's a short format so you've got to switch on. You have got to be on your A-game, and I was very focused tonight."
Van Gerwen sweeps to win
Like Littler, there was a comfortable victory for Michael van Gerwen who whitewashed Noah-Lynn van Leuven 5-0.
The three-time Grand Slam winner converted half of his checkout attempts - his highest being a 124 - in a comfortable performance against the debutant.
Van Gerwen's next match in Group G sees him face Gary Anderson after the Scot stormed past Ryan Joyce 5-1 in his opener.
Anderson tallied a 113.2 average and pinned 16 tons in a masterful display.
"That wasn't bad after 17 years (at the Grand Slam)," Anderson said.
"If my floor game comes on to the stage, there could be trouble, but what will be will be!"
Elsewhere, Michael Smith claimed victory over Mensur Suljovic in Group E, Micky Mansell upset James Wade 5-3 and Peter Wright and Dave Chisnall were beaten by Martin Lukeman and Connor Scutt respectively.
