LONDON — Martin (The Hitman) Kampmann stopped veteran Jorge (El Conquistador) Rivera with an early guillotine choke hold to celebrate his return to action from knee surgery Saturday in a preliminary fight at UFC 85 at the Millennium Dome.

The Danish mixed martial arts middleweight, who is now based out of Las Vegas, took Rivera down early and worked him from above. The guillotine hold forced Rivera (15-7) to surrender at 2:44 of the first round.

Kampmann (13-1) had endured two knee operations since his last fight at UFC 68 in March 2007.

The main event was to pit former welterweight champion Matt Hughes against Brazilian Thiago Silva.

The card was plagued with problems from the start. The main event was originally to have featured former light-heavyweight champion Chuck (The Iceman) Liddell against Mauricio (Shogun) Rua, but the Brazilian was shelved because of knee surgery. Rashad Evans was brought in as a replacement, but then Liddell tore a hamstring.

Evans was eventually pitted against James (The Sandman) Irvin, but Irvin broke a foot. In all, eight fighters fell off the card, including Chris (The Crippler) Leben, whose preparation was disrupted by jail time arising from a parole violation.