Known as "Lil' But Bad", Johnston turned pro in 1993 and fought for the WBC Lightweight Title against Jean Baptiste Mendy in 1997, winning a close split decision. Johnston defended the title three times before losing the belt to Cesar Bazan in 1998 in a close decision. In 1999 he won a rematch against Bazan in another close decision. He defended the title four times, including a victory over Angel Manfredy, but lost the belt in a loss to José Luis Castillo in 2000 via majority decision. The loss was declared the 2000 Upset of the Year by Ring Magazine, as Castillo was relatively unknown at the time and Johnston was thought to be over the hill. It wasn't until a couple years later that the world would know how good of a fighter Castillo was. Later that year, in an attempt to regain the belt, Johnston rematched Castillo. In a bizarre ending, Johnston was originally declared the winner by Majority decision. Several minutes later it was discovered that Judge Ken Morita's scorecard (originally 115-114 Johnston) had been added incorrectly and should have read 114-114, thus making the bout a draw and allowing Castillo to retain his title. This was to be Johnston's last shot at a major title.

Shamba Mitchell.................................Fight #12

Fred Valera............................................Fight #13

Corey Johnson.....................................Fight #14

Howard Grant.......................................Fight #15

Paquito Openo.....................................Fight #16

Jesus Rodriguez..................................Fight #17

Mark Fernandez...................................Fight #18

Jean Baptiste Mendy.........................Fight #21

Hiroyuki Sakamoto..............................Fight #22

Saul Duran.............................................Fight #23

George Scott.........................................Fight #24

César Bazán #1......................................Fight #25

César Bazán #2......................................Fight #27

Aldo Nazareno Rios..............................Fight #28

Angel Manfredy.....................................Fight #29

Julio Alvarez...........................................Fight #31

José Luis Castillo #1............................Fight #32

José Luis Castillo #2............................Fight #33

James Crayton.......................................Fight #35

Alejandro Gonzalez...............................Fight #37

Ever Beleno.............................................Fight #38

Juan Lezcano..........................................Fight #39