The Kiwi superstar, the tournament's star attraction, was left red faced after producing one of the biggest howlers in recent rugby league memory in New Zealand's 42-24 victory over Samoa on Sunday.
The dual international, in his first game for the Kiwis since the Anzac Test of 2008 after defecting to union, looked set to cap a solid performance with a try with 12 minutes to play.
It started with a brilliant run which left defenders sprawled all over the field.
He crossed the line totally free of pressure, before inexplicably running deep into the narrow in-goal before slipping and putting a foot into touch before he could ground the ball.
Williams' look of embarrassment told the story before the try was officially disallowed by the video referee.
"Embarrassed to not score, but nothing wrong with a lil humble pie," Williams tweeted shortly after the contest.
The ruling was met with jeers from the near-14,000 fans packed into Warrington's Halliwell Jones Stadium who had been baying support for a spirited Samoa side.
Given it had little bearing on the result, it even attracted a laugh from coach Stephen Kearney.
"He might want to check his boots next time," joked Kearney.
"It was a good indication of that period of the game."
Williams had been strong throughout the match defensively, while two of his trademark offloads led to tries.
His howler provided further entertainment in an already-thrilling Group B match that also featured a hat-trick to Warriors winger Manu Vatuvei.
In Sunday's other match, Gold Coast flyer David Mead was left devastated after missing a late penalty in front of the posts to cruelly deny Papua New Guinea a first World Cup victory in 13 years.
The Kumuls fell 9-8 to France on Sunday despite scoring two tries to the victors' one in their Group B encounter in Hull.
Star NRL winger Mead failed to convert both of PNG's tries but had a golden chance to secure victory after his side earned a penalty 25m out from the French tryline with a minute to play.
But he failed to factor in a strong breeze at Craven Park and his effort sailed wide as coach Adrian Lam and high performance director Mal Meninga watched on in horror.
Lam said it was unfair to blame Mead, who assumed the responsibility with the squad not featuring a specialist goalkicker.
"David is devastated," Lam said of Mead, who has battled back from suffering a fractured vertebrae earlier this year.
"He's a great young man and we spoke with him about how he's not to blame. He is a big part of our side.
"He's not a week in, week out goalkicker and we don't have one. That's the problem.
"He's blaming himself but there are a couple of other things we could have done better."
Lam said he was both proud and disappointed with the performance.
The rugby league-mad nation still has a chance to progress from the group, which also features New Zealand and Samoa.
"If we kick the goal it's a great night, so now we have to pick ourselves back up off the ground. We couldn't convert our opportunities," Lam said.
France halfback William Barthau kicked what proved the decisive field goal with 15 minutes to go as France avenged losing to PNG at the 2000 World Cup, the Kumuls' last Test win.
French playmaker Thomas Bosc opened the scoring in the sixth minute before PNG winger Nene McDonald responded with a try in the corner.
The Papua New Guineans started the second half with new resolve, a forced Mickael Simon knock-on resulting in the ball being spread left and winger Josiah Abavu crossing.
Bosc brought the scores level with a penalty 20 minutes from time before and fellow Barthau nailed a 35-metre field goal.
France coach Richard Agar knew his side was lucky to escape with a win.
"If I'm honest, I wouldn't have had many complaints had we lost," he said.