The importance of the 13-9 victory should not be underestimated, even if their performance from Nos 15 through to one should hold few fears for future opponents. England are now in the box seat in arguably the tournament's toughest pool. They have games at Dunedin against Georgia and Romania to hone their faltering attack patterns before a powderkeg match-up with Scotland at Eden Park on October 1.
It is Argentina, who head to Invercargill for a match with Romania before meeting the Scots in Wellington, who face the anxiety of knowing another loss is likely to send them home early. From third place four years ago, it would be a fall from grace.
It was those Pumas who provided Johnson with a handy reference point: "In '07 France [who lost to 12-17 to Argentina in the first match] would have bitten your arm off to win that game. In the circumstances, that was a good win, a fantastic win because [we] were six points down. It was stop-start ... it was difficult, but we got over the line."
Johnson has the win, but also selection issues. Ben Youngs gave the side more direction and spark from the base of the ruck when he replaced Richard Wigglesworth at halfback. His selection from here should be a no-brainer.
Then there is the question of what to do with Jonny Wilkinson. He had an off night. It would be unusual for him to have two.
"You concentrate on what you control and for me that's kicking the ball. Today it felt good, felt right but it wasn't going over. You can't let these things faze you," Wilkinson said.
More worrying was the way he telegraphed whether he was going to pass, run or kick. His game looks regimented and forced in comparison to Toby Flood's.
England's vaunted three-quarters - Manu Tuilagi, Chris Ashton and Delon Armitage - were massively disappointing. Only Ben Foden looked remotely capable of unpicking Argentina's defence, but then didn't know what to do once he had.
Georgia and Romania give them a chance to regain some confidence.
The loosies, too, were shaken by Argentina, but they are unlikely to face such an intense character examination in the next three weeks.
James Haskell, whose place could be under threat from a returning Lewis Moody, admitted they failed to deal with Argentina flooding the breakdown.
"Argentina are a team of a lot of old, experienced, tough men. They caused a lot of havoc at the breakdown and we didn't adjust as we should do. We didn't play to the referee as we should have done. We got penalised quite a lot, which was difficult. They make everything into a fight. If you're not 100 per cent accurate you give away penalties."
In a tough pool, Haskell warned fans not to expect the floodgates to open. "There's not an easy game at this tournament. As soon as people realise that there won't be as much shock on people's faces. Argentina, Romania, Georgia, Scotland - they're all tough games."
