And while the All Blacks pushed hard they could not muster another response meaning the match ended as a draw, handing a 2-1 series victory to the tourists.
That 1971 side remain the first and only squad to emerge victorious from the Land of the Long White Cloud.
And while their forward pack stood up to the bruising Kiwi side throughout the four-match series, more often than not it was the boot of Barry John that saved the day.
But in that last Test it was Williams who stepped up to the plate to produce the goods and claim a historic series success that is still revered to this day.
Interestingly, the manager of the 1971 Lions squad, Dr Doug Smith had predicted a Lions series win at the start of the tour with a 2-1 margin, with one test drawn-which is exactly what happened.
And Lions No.8 Mervyn Davies admitted he and his teammates were desperate to make sure that the series was sealed in that fourth and final Test.
"If you want to be seen as a great rugby player you have to prove yourself on the toughest playing fields of all, New Zealand," he said.
"Just like every other Lions side before us, we wanted to win - the real difference with us, though, was that we actually believed we could.
"Everyone has this image of the 1971 Lions playing wonderful, expansive rugby throughout New Zealand, but the real truth was that the method wasn't important to us, it was just the result we wanted.
"And when it came to the crunch, we shut up shop and played a tight game. It was a question of survival, with the boot of Barry John kicking us out of trouble for most of the time.
"The record books show that we won the Series with two victories and a draw, but I still struggle to this day to understand how we managed to keep the All Blacks at bay."