It took a last-minute extra-time drop goal by fly-half Jonny Wilkinson to seal the win for England and Johnson was lavish with his praise of the young England star.
England were leading 14-5 at half time, but Australia fought back in the second half and a successful penalty kick by Wallaby centre Elton Flatley on the stroke of full time, drew the teams level at 14-14, taking the game into extra-time.
Flatley repeated the feat in the second half of extra-time with two minutes to go, but it was not to be, as England drove back up the field at the restart – allowing Wilkinson room to put the final kick over.
"We had a lead and we lost it and to come back in extra-time and to hold out and Wilko [Wilkinson] at the end, brilliant. I can't say enough about it," said an emotional Johnson.
Johnson admitted that they had been outplayed in the second half and gave credit to the Australians for a spirited performance. And again the veteran lock singled out Wilkinson for special praise.
"We were frustrated in the second half," he said. "You've got to give credit to Australia, they are a very good team, they came back and made it difficult for us.
"With 20 minutes of extra-time it can go anyway, but 'Wilko' was there and right at the death you would have no-one else, would you?"
The win is the most significant England sporting achievement since winning the Football World Cup in 1966 and for Johnson and a number of other England veterans, the last chance for World Cup glory.
"I'm just happy for the players," he said.
"They've put so much into it and the management, they've put their heart and soul into it … It couldn't have been any closer, I'm just glad we were on the right side of it."