In 1999, Guymon had his first professional fight against Zach Turnage with the fight resulting in a draw after fighting in three five-minute rounds and a five-minute overtime. He won two straight before opening the eyes of the matchmaker for the
King of the Cage promotion who offered him a fight against up and comer,
Diego Sanchez. Guymon took the fight and lost by armbar submission with three seconds left in the first round. Guymon's next four fights came inside the
King of the Cage promotion all wins and all of them coming by submission in the first round. With the four wins he improved his overall record to 6-1-1 getting him signed to the
IFL. He made his debut taking on
Pat Healy losing via a split decision. Guymon then returned to
King of the Cage and won five straight fights, the last one being for the
King of the Cage Welterweight Championship just three weeks after his suicide attempt.
Ultimate Fighting Championship Four days after defending the
King of the Cage Welterweight Championship against
Quinn Mulhern, Guymon received a call from the
UFC about signing a contract. Guymon accepted and signed onto a four-fight deal. He lost his UFC debut on January 11, 2010, in
Fairfax, Virginia, at
UFC Fight Night 20 against 20-year-old
Canadian,
Rory MacDonald. The fight stayed standing for the most part but ended when Rory took the fight to the ground and
submission submitted Guymon with an
armbar near the end of the first round. Guymon defeated
Yoshiyuki Yoshida on May 8, 2010, at
UFC 113 by unanimous decision. Guymon faced
Daniel Roberts on October 23, 2010, at
UFC 121. Guymon would go on to lose the fight after Roberts locked on an anaconda choke, following with a gator roll that tightened the squeeze forcing Guymon to tap. Guymon next faced
DaMarques Johnson on January 22, 2011, at
UFC Fight Night 23 where he was injured early into the fight. He lost via verbal submission in the first round. After the fight, due to rupturing two discs in his back, Guymon announced his retirement from MMA.
Post-UFC Guymon came out of retirement on March 16, 2012, dropping down to the
Lightweight division where he defeated Chris Leyva by TKO due to punches in the second round at BAMMA USA: Badbeat 5. In his second fight at Lightweight in Bamma USA he beat Mike Dizack by split decision. Guymon faced
Savant Young at
Bellator 85. He suffered the first knockout loss of his career after a left hook from Young put Guymon out cold, just under a minute into the second round. After the fight, Guymon was taken to the hospital, where the doctor noticed he had fracture of the orbital, cheekbone and jaw. The doctor advised Guymon to never compete again in any combat sport. Days after his first Bellator win against Aaron Miller on November 2, 2013, Guymon announced his retirement from MMA for the second time. ==Personal life==