Photo: Contributed - Jeff Chiu

Rory MacDonald, right, elbows BJ Penn in the first round of a welterweight mixed martial arts bout at a UFC on Fox event in Seattle, Saturday, Dec. 8, 2012. MacDonald won by unanimous decision. (AP Photo/Jeff Chiu)

Canadian welterweight Rory (Ares) MacDonald used brutal body shots to batter B.J. (The Prodigy) Penn en route to a convincing decision over the former UFC champion on Saturday.

The 33-year-old Penn seemed close to folding in the second round as the blows to the body took their toll. But the undersized Hawaiian showed a huge heart and finished the fight.

MacDonald, a decade younger, was bigger and more powerful. Penn gave it his all and never stopped coming forward, but always at a cost. His lumpy, swollen face told the story and he was taken to hospital after the fight to be checked out.

There was a fractious leadup to the contest but the two shook hands briefly as the bout ended. The judges scored it 30-26, 30-26, 30-27 for the Montreal-based fighter, who established his credentials as a 170-pound contender if not a fan favourite.

"A huge role model for me ... He's a hero for me," MacDonald, who was booed during his post-fight interview, said of Penn.

But all that respect goes out the window when he steps into the cage, the young Canadian added.

MacDonald (14-1) ran his winning streak to four in a supporting fight that had a main event feel to it. Penn (16-9-2) has now gone 1-4-1 since the start of 2010.

In the main event of a highly entertaining televised card at KeyArena, lightweight champion Benson (Smooth) Henderson dominated Nate Diaz in a lopsided 50-43, 50-45, 50-45 decision.

It was a mature, impressive performance by the 155-pound champion, who has struggled to win respect since beating Frankie (The Answer) Edgar in two close title fights earlier this year. Henderson showed all the weapons in his arsenal, and then some. In the third round, he essentially did the splits to evade a submission attempt.

In addition to a takedown and scything kick, Henderson used his grappling to control Diaz at the fence in a first round that saw the two get in each other's faces as the bell sounded. Diaz's face was already showing damage and it got worse with a short elbow in the second.

Diaz raised his arm after the third round, but it was all Henderson at that point. Diaz, a good striker with a black belt in Brazilian jiu-jitsu, was never allowed to get his game going.