Johnson had been struggling with a lower back strain that kept him out of games for the first half of the team's camp. His velocity was down as much as five mph, and the righty said it felt like he was throwing "underwater."
"I went through some periods in the spring where I was kind of going, 'Boy, I don't know if he's going to quite get there,'" Showalter said. "We went through a long period there with him where we were really being cautious with him."
But Showalter said there was an outing towards the end of spring where Johnson showed he was 100 percent, and he could see it on the closer's face.
Any concerns about Johnson's health are in the past, as he's established himself as one of the game's premier closers by posting a Major League-best 15 saves and pitching to a 0.92 ERA.
Dating back to last season, Johnson has converted 23 consecutive save opportunities.
"Jimmy never cheated the process," Showalter said. "That's why he is getting a return."
Johnson has been far from the typical closer, as he's used his sinker to get ground balls rather than trying to strike every batter out.
"When you go out and close one-run games facing the [Nos.] 2-3-4 of a tough lineup in the American League East on the road, that's a difference maker," Showalter said.