He didn't have a poor game - he ran for 140m in 17 carries and produced three tackle breaks, 29 tackles and five offloads - but it also wasn't his best and Australia's tactic of sending multiple defenders at him worked. Even so, his five offloads were only one less than Australia's total.
"Some of the stuff didn't come off, but that's Sonny," coach Stephen Kearney said. "He wants to try to make an impact on the game and he was doing that right to the end."
It dashed Williams' chance to become the first person to win the World Cup in both rugby union and rugby league.
"It was never about that," he said. "It was just about having no regrets when I retire. Just being a part of it ... just very disappointed right now.
"You win some, you lose some. It's been a privilege to put the Kiwis jersey back on. Just really disappointed for the fans back home and our families.
"I'm heartbroken ... I left it all out there today. That last 20 minutes was disappointing. I tried to overplay my hand and try to come up with something special and it wasn't to be. I definitely feel bad for the brothers but, full credit to Australia, they were just too good today," he said.
Williams might play for the Kiwis again next year after agreeing to return to the Roosters for another season but it's doubtful he will be back for another World Cup campaign. He has indicated he will return to rugby union in 2015 in the hope of playing for the All Blacks and their defence of their World Cup before attempting to win Olympic gold in sevens in Rio in 2016.
By then he will be 31 and he earlier told the Herald he might be ready for retirement at the end of 2016.
Kiwis assistant Ivan Cleary said Williams was "at the top of the tree in terms of elite players in our game and that's coming from a guy who hasn't played for five years. That in itself is phenomenal. Just the way he carries himself, the way he prepares, it's a pleasure to work with someone like that."
