Reynolds, 25, went a combined 6-5 with a 2.29 ERA in 60 appearances -- 39 at Class A Advanced Modesto, 21 at Double-A Tulsa. Johnston, 25, went 2-4 with a 3.69 ERA at Tulsa.
The two have different approaches. Reynolds struck out 87 and walked 17 in 74 2/3 innings during the regular season. Johnston induced 1.83 groundballs for every fly ball.
Both are pitching for the Scottsdale Scorpions.
Team scouting and player development directors, AFL director Steve Cobb and his staff selected the teams for the event. Every Major League organization is represented. Saturday's game can be seen on MLB.com and MLB Network at 6:15 p.m. MT.
Thomas Harding is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.