Johnson twirled four innings of one-run ball as he led the Mesa Solar Sox to a 6-1 win over the Salt River Rafters on Wednesday at Sloan Park.
The No. 7 prospect in the Cubs system threw 47 of his 65 pitches for strikes, gave up four hits, walked one and struck out six.
"It felt really good. I was throwing everything for strikes, which I think was the game-changer for me today," Johnson said. "Cael [Brockmeyer] did a great job behind the dish, and my defense, as usual, came through strong behind me."
Johnson struggled in the early stages of the AFL because he was still making some mechanical adjustments and trying to find a feel for his slider, a pitch he had trouble locating for the bulk of the season.
"I actually threw it a lot back in 2014, but they wanted me to work on my changeup this year, and now that I feel confident in my changeup, I kind of lost my cutter," Johnson said. "Just getting the feel for that again was huge, and I think that kept people off balance."
Over his final two AFL starts, Johnson tallied nine innings of work and allowed one run on nine hits. He walked two, struck out 10 and lowered his ERA from 8.04 to 5.47.
"I think that honestly it all clicked for the last two outings. I was trying to put all that together and finally it all clicked," Johnson said.
With newfound confidence in his slider, Johnson concluded the AFL on a high note and enters the offseason looking for ways to improve on what was a stellar 2015 campaign.
Johnson missed the first two months of the season with a lat strain, but once he got on the mound, he went 6-2 with a career-low 2.08 ERA in 16 starts with Double-A Tennessee.
"I'm just going to go out there and give my team the best opportunity to win," Johnson said. "That was my goal last year and I feel like I went deep into games and I gave us the opportunity to win almost every time I went out. So, for me, it's just keep progressing and cut down the walks, throw strikes and just be the best quality starter I can be."
-- Marlins prospect Austin Dean went 2-for-4 with an RBI. Dean has multiple hits in two of his last three games and is hitting .323.
-- Fellow Miami farmhand J.T. Riddle had a big day at the plate, going 1-for-4 with three-RBIs, including a two-run ground rule double in the sixth.
-- With their loss, the Rafters were eliminated from contention and the Scottsdale Scorpions clinched the AFL's East Division. The Scorpions will play against the Surprise Saguaros in the championship game on Saturday at 3:08 pm ET.