Johnstone says it was a "fair" result.
"I felt good – there were a couple of saves in there," Johnstone said. “It is nice to do that and to get a point, but it would have been better with three.
“It is good. That's what I'm there to do, really. It is nice that I had a couple of nice saves in there, and we get that draw.
“We worked hard, all of us, for that [clean sheet]. When called upon, luckily I was there to do the job today, but it's a team effort for that clean sheet. It's a good point.
“[A draw] is a fair reflection, really," Johnstone said. “We had some good chances, they had some good chances.
“Premier League games are never easy so I think it's a fair result. You never know what can happen on matchday.
“We go in to get three points and win the game, and I'm sure they do too. They had a couple of good chances and we had some good chances.
“A point was probably fair."