To add to the feelings of frustration, Williams was denied a try in the final few minutes when he thought he'd grounded the ball.
But the fact is the Roosters live to fight another day. And Williams remains on track to add to his incredible legacy by claiming a second premiership in as many years in his cameo career for the Roosters before returning to rugby union and the All Blacks.
"It's pretty tough," said Williams when describing his emotions post-match. "The way they were rolling through our ruck, it wasn't a great feeling out there.
"We just clinched it at the end there and, thankfully, that's how footy goes sometimes. Thankfully the coin landed in our favour.
"One win away from the grand final. It's a big game this week and we've got to turn our attention to Souths who are in great form and are at another level."
Already the mind games have started. Roosters five-eighth James Maloney believes the Rabbitohs might find the burden of expectation too much to handle.
Souths haven't appeared in or won a grand final since 1971 and for the past two seasons have fallen at this same hurdle - a game short of the premiership decider.
Maloney knows the pressure will all be on Souths, it's simply up to the Roosters to ensure the Bunnies players feel the heat.
"Obviously they've had a couple of years where they've come so close and no doubt that will be playing on their minds, so we'll see how it goes," Maloney said.
"Hopefully it comes into play. Hopefully we can put ourselves in a position in the game where that can start weighing on their minds. But it won't happen until we start really well and we make them go to some dark places."