O'Neil went into Monday night's fixture at the London Stadium aware that he could be sacked if his side suffered a third successive defeat and 10th in 15 top-flight fixtures during 2024-25.
Although Wolves had their moments versus the Hammers in an even game, goals from Tomas Soucek and Jarrod Bowen ultimately proved to be the difference.
The latest setback leaves Wolves four points adrift of safety ahead of mammoth fixtures against Ipswich Town and Leicester City across the next two weeks.
However, Wolves - not for the first time across the last 15 months - felt that several pivotal decisions went in West Ham's favour during the second half.
Does O'Neil have a point?
Replays showed that the corner that led to Soucek's goal should have instead been a goal kick, while Wolves seemingly had a case for a foul in the build-up to Bowen's second after Konstantinos Mavropanos jumped and held down Santiago Bueno when challenging for a high ball.
Up the other end, Wolves were denied a penalty when Goncalo Guedes went down under a clumsy challenge from Emerson Palmieri. Wolves would score from their next attack, making this decision irrelevant.
When trailing 2-1, Jean-Ricner Bellegarde was clipped inside the area. VAR deemed that there was not enough contact for a penalty to be awarded.
What did O'Neil have to say?
Speaking to Match of the Day, O'Neil said: "We were OK, we were solid, probably had the better chances and a lot of decisions go against us, an awful lot of decisions go against us in a big game, big moments, you need some of them to go your way and you hope they do but today they didn't."
He added: "I think there's four. I don't think it's a corner, the corner they score from. I think it comes back off [Aaron] Wan-Bissaka.
"There's a blatant foul in the build up to West Ham's second goal on [Santiago] Bueno in the middle of the box, unbelievably blatant. Really surprised that wasn't given first then checked
"Then the penalty is a blatant penalty, Emerson on a yellow card, tracking back, has a big shove into the back of Guedes which causes him to stand on ball.
"Small contact but enough to make Jean-Ricner Bellegarde fall over. Disappointed they didn't go our way but we have our own battles to fight."
Pressure will now mount on O'Neil with Wolves' hierarchy left to decide whether the Englishman will get at least one more match to try to kick-start Wolves' season.
Written by
Darren Plant