Two days after responding to critics on Twitter, Johnstone saved a penalty in an impressive display that earned Albion a point against Derby County.
Before the match Johnstone had tweeted 'should save everything according to some ppl' and 'must be so easy from where you sit' in response to criticism he should have saved some of the goals Albion had conceded this season.
But his name came booming out of the away end both during and after the draw, in an obvious effort to restore the relationship between the fanbase and the club's No.1.
"I heard them singing, and it gave me confidence," said Johnstone. "It is what it is, fans praise you, they say other things, you see a lot of stuff now.
"That's just social media. It was earlier on in the week and it's finished now.
"It's someone's opinion. You have your opinion on me, you might think I'm rubbish. It is what it is.
"All that matters to me is my team-mates, my manager, my goalie coach – and when the fans are loud like that at away games, singing your name and about the manager and the team that also gives us the extra edge to keep going and get an extra goal to go and win it."
When Johnstone was asked if it was difficult being on social media as a footballer, he said: "It depends if you look at it all or not. That's just social media these days and you can't control it."
And he said he wouldn't let those criticising his performance force him off the platforms.
"Of course not," he said. "I'm not the only one. Yeah I'll stay on it, it's water off a duck's back.
"I had a lot of positive messages, I appreciate that. I won't be coming off Instagram and Twitter for a few comments."
Slaven Bilic also leapt to the defence of his keeper, and thanked Johnstone for keeping Albion in the game with Derby.
"I disagree with the fans that he was the one to blame for the Reading goal, we had to close (Ovie) Ejaria," said Bilic. "The strike was magnificent.
"It's a team sport, but we have to thank Sam that he kept us in the [Derby] game, not only with the penalty but with the double save.
"Ok they're keeper had to make a few saves at 1-0 but Sam was great today and I like him a lot and he knows that. I want my keepers to be confident."
Excluding shoot-outs, Johnstone has now conceded just four of the ten penalties he's faced as Albion keeper, but he was humble about his save from Martyn Waghorn's second spot kick.
"To be honest, the second penalty with the same taker you're trying to double-guess each other," he said. "Is he going to go the same way because he scored? Am I? Luckily
"I dived the right way, saved it and we've earned a point out of it. When it's the same taker it's a bit more difficult because you're double-guessing.
"We do our homework on them, but we don't do homework on someone taking it twice in the same game.
"It's a bit of luck but thankfully it went our way today and we managed to get something out of the game."