Jake O'Brien was formerly a fighter in the UFC's heavyweight and later light-heavyweight divisions. He was cut from the promotion's roster after a loss to the heavily favored prospect Jon Jones. He has since picked up victories over Dave Hess and Toni Valtonen after leaving the UFC.
For his first major fight since his UFC tenure, O'Brien took a big step up in competition, facing former Strikeforce light-heavyweight champion Gegard Mousasi in the opening semi-finals of the Dream 2010 light-heavyweight tournament. O'Brien came in severely overweight for the bout and was deducted a portion of his purse. To add injury to insult, Mousasi finished O'Brien with a tight standing guillotine choke under a minute into the fight.
- Jake O'Brien vs. Herc Hayes
- Jake O'Brien vs. Heath Herring - The fight was the UFC debut of Heath Herring.
- Cain Velasquez vs. Jake O'Brien - Cain Velasquez came into the fight undefeated of course. They had met before in a wrestling competition, years before their MMA careers.
- Jake O'Brien vs. Christian Wellisch - The fight was the light-heavyweight debut for both fighters.
- Jon Jones vs. Jake O'Brien - O'Brien was cut after the fight.
- Gegard Mousasi vs. Jake O'Brien - The fight was in the opening round of the Dream light-heavyweight grand prix. O'Brien came in severely overweight.