Johnson said the 83-point loss was particularly frustrating as it was Grover's 150th match, a player much-admired among the Purple Haze faithful.
"We were very disappointed in our effort today. We actually thought we played all right in the second quarter and we almost outscored them, but we were just very disappointed with the effort and we let down our fellow teammate Antoni Grover on his 150th game," he said.
"The boys are hurting with the loss."
"It's been happening over the last few weeks. We had a good quarter against Adelaide last week and then came back in the last quarter and then we faded away.
"All we can do is take the positives out of the game on Monday and then just move on and concentrate on next week's game against Sydney."
Johnson also said skipper Matthew Pavlich gave his side a rev-up at quarter-time.
"He said we were in it and we didn't capitalise on our chances and we had too many turnovers. The boys knew that," he said.
"In the second quarter, we stayed with them, but then they just came out in the second half and just dominated and we couldn't get our hands on the ball.
"We turned the ball over heaps and we have to fix it on the training track this week."
Johnson said he was unsure how the players would pick themselves up from a loss like that, but he remained positive that they had to fight their way out of it.
"It's a hard one, because we're zero and four now and it was a big loss today, so we can't say anything at the moment," he said.
"All we've got to do is be positive and concentrate on next week's game."
Although he collected 24 touches against the Saints and has been one of Fremantle's better players so far this year, Johnson said he was annoyed with some of his efforts.
"My own game, I'm disappointed in a few efforts, where I turned the ball over a bit, especially in the third and last quarter," he said.
"I actually pride myself on my skills and my footy smarts, but my skills let me down today and it's been a problem for the team for the whole year.
"The last couple of games, I've been playing in the backline and I like it back there."
