Strikeforce lightweight champion Josh Thomson will face interim champion Gilbert Melendez in a five-round rematch at Strikeforce “Evolution” on Dec. 19 at the HP Pavilion in San Jose, Calif.

The bout, which will unify the promotion’s two lightweight titles, had been twice scheduled and cancelled due to injuries sustained by Thomson in 2009.

Thomson’s shutout decision over Melendez in June 2008 is considered one of the high points of the San Jose fighter’s career.

As a 3-to-1 underdog, the American Kickboxing Academy product established confidence with the Pride Bushido star early, and actively used lateral movement to keep Melendez at bay throughout the 25 minutes. The loss marked only the second in the highly touted Melendez’s career, and solidified what many suspected of the Thomson’s potential in the lightweight division.

In his last performance in September 2008, Thomson, 31, made quick work out of an overmatched Ashe Bowman in a non-title bout, cutting down the Lion’s Den prospect in only 74 seconds at Strikeforce’s second event at the Playboy Mansion.

Melendez earned the interim title with a second-round technical knockout of Rodrigo Damm in April 2009. The voracious 27-year-old wrestler defended the title in August when he demolished Mitsuhiro Ishida with strikes inside three rounds. Melendez also holds key victories over standouts Clay Guida and Tatsuya Kawajiri.

Thomson-Melendez II joins a previously announced roster that includes a main-event middleweight bout between Cung Le and Scott Smith, as well as the promotional debut of Muhammed Lawal against Mike Whitehead at heavyweight.

Strikeforce “Evolution” will be broadcast live on Showtime.