Miller in the main event of UFC on FX 1 on January 20, 2012. After dropping Miller in the early going, Guillard was submitted in the first round. Guillard next fought Fabrício Camões on July 7, 2012 at UFC 148. He won the fight via unanimous decision. Guillard fought Donald Cerrone on August 11, 2012 at UFC 150, and was knocked out early in the first round after clipping Cerrone with a big left hand. He received a $60,000 Fight of the Night bonus award for his effort. This was the first knockout loss of his career. Guillard was scheduled to face Jamie Varner on December 15, 2012 at The Ultimate Fighter 16 Finale. However, Varner fell ill the day of the event and the bout was scrapped from the card. The bout with Varner was rescheduled for December 29, 2012 at UFC 155. Guillard was taken down by Varner several times in their bout, losing a split decision. Guillard faced Mac Danzig on July 27, 2013 at UFC on Fox 8. He knocked Danzig out in the second round. The win earned Guillard his third Knockout of the Night bonus award. Guillard faced Ross Pearson on October 26, 2013 at UFC Fight Night 30. The fight ended in a no contest when Pearson was deemed unable to continue after being cut on the forehead by an accidental illegal knee. As a result of the controversial result, a rematch was booked for UFC Fight Night 37 at March 8, 2014 in London. However, Pearson pulled out of the fight due to injury and was replaced by Michael Johnson. Guillard lost the lackluster fight via unanimous decision and was subsequently released from the promotion. World Series of Fighting On April 7, 2014, World Series of Fighting executive vice president Ali Abdel-Aziz confirmed Guillard had signed a multi-fight contract. Guillard made his debut at WSOF 11 on July 5, 2014 against Gesias Cavalcante. He won the fight via TKO in the second round. Guillard was expected to challenge Justin Gaethje for his WSOF Lightweight championship on November 15, 2014 at WSOF 15. However, Guillard missed weight for the bout and it was changed to a catchweight affair. Guillard lost the fight via split decision. On April 30, 2015 Melvin was released by the World Series of Fighting. His manager, Malki Kawa, announced the news on Twitter: "I just received what I asked