Nick Diaz proved that he is no minor league champ on Saturday in the main event of UFC 137.

The last Strikeforce Welterweight champion overcame a slow start to dominant the final two rounds against UFC legend, B.J. Penn, as Diaz picked up a unanimous decision win for perhaps the biggest win in his career.

Diaz survived the opening round as Penn came out with a fast start, using dirty boxing and grappling to control the round. Penn had Diaz’ back at one point, but Diaz was able to get out of the dominant position and get into the later rounds, where he started to work his boxing.

Diaz used relentless jabs and combinations to pick apart the tiring Penn, who ended up with a busted nose and bruised face before the final bell sounded. The decision wasn’t really in doubt, as Diaz had clearly closed out the final two rounds.

Following the win, Diaz called out UFC welterweight champion, Georges St. Pierre, whom Diaz was originally scheduled to face before being pulled from the title bout by the UFC as a disciplinary action for missing pre-event press conferences.

Still, Diaz is likely in line for a title shot against GSP or Carlos Condit, who will be fighting for the title in early 2012.

Penn announced his retirement from the sport following the loss, his third in his last five fights. Penn will go down as one of the all-time greats as he held titles in two different weight classes and was arguably the top pound-for-pound fighter in the world during his prime.

For full UFC 137 results, check out the jump.

UFC 137 Results

Saturday, Oct. 29, 2011

Mandalay Bay Events Center, Las Vegas

Nick Diaz def. B.J Penn by unanimous decision

Cheick Kongo def. Matt Mitrione by unanimous decision

Roy Nelson def. Mirko “Cro Cop” Filipovic by TKO at 1:30, R3

Scott Jorgensen def. Jeff Curran by unanimous decision

Hatsu Hioki def. George Roop by split decision

Donald Cerrone def. Dennis Siver by submission (rear naked choke) at 2:22, R1

Bart Palaszewski def. Tyson Griffin by KO at 2:45, R1

Brandon Vera def. Eliot Marshall by unanimous decision

Ramsey Nijem def. Danny Downes by unanimous decision

Francis Carmont def. Chris Camozzi by unaimous decision

Clifford Starks def. Dustin Jacoby by unanimous decision