The Dark Blues barely had a sniff against Ireland in an awful first-half display at Murrayfield but somehow went in at the break a mere three points down. Ireland did add five more with Craig Gilroy's try three minutes into the second period but that concession was enough to finally shake the home side from their lethargy.
Having surrendered 78% of the possession and 80% of the territory to Declan Kidney's men in the first half, they responded in spectacular fashion to force themselves further up the pitch and into kicking range.
And it paid crucial dividends as scrum-half Greig Laidlaw slotted over four perfect penalties to confirm a stunning 12-8 victory.
Johnson was happy with the victory – Scotland's first over Ireland since 2001 – but admitted improvements are urgently required ahead of Wales in a fortnight. He said: "We have got to be honest and say that it wasn't perfect from us.
"At half-time I felt like we must have watched Ali and Foreman or something. We were lulling them into some false sense of security. My neck was getting sore looking down to one end of the pitch.
"It's a funny game. I've played in games when I've been on the other side. It puts a bit of pressure on the team that should be in front. We went in at 3-0 down and I would have taken that.
"So we took it and we took our chances. We will enjoy the next 24 hours but we will also acknowledge that we have got to work on a few things."
Scotland captain Kelly Brown played as crucial a part as any of his team-mates as he cajoled a side under the cosh into a winning position.
But, with an eye on the stats that showed even at full-time, the Scots had managed just 29% of the possession and were forced into 128 tackles just to keep the Irish at bay, he also was under no illusions about their standard of performance.
"We are really happy to get the win but we know we have to improve," he said, "because if we play like that in two weeks' time against Wales, then we will not win that game."
The Scots had gone into the match looking to rid themselves of another hoodoo having not managed back-to-back wins in the same 12 years since they had last toppled the Irish.
The coach – whose side remain joint-top try scorers with Wales – said: "I think we are in it. There's no doubt we can compete. We have shown that once we get things right, we can hurt sides with the ball.
"But unfortunately in the first three games we have lost possession and territory.
"If we get that right we have shown we can score tries against quality sides and we have shown we can defend like hell."
Lock Jim Hamilton, who was named man of the match, said: "I think you can see what it means to the boys and the supporters here. That is a massive win for us.
"The support here was absolutely outstanding and you saw what it meant to the boys hanging on in there at the end.
"We have put a lot of work into our line-out and scrum. I thought our scrum was absolutely immense.
"I think a special mention has to go to Geoff Cross – he has come in and done a magnificent job. Credit to all the forwards.
"We really dug deep and I think you can see that means a lot to us."