Vitor's main weaknesses are his cardio and his chin. The best way to beat him is to stall the fight until the second or third round, at which point he is exhausted and can be finished easily. In the first round, Vitor is one of the 3 most dangerous fighters ever in any weight division. Also, one hit to the chin is all it takes to KO him. The guy crumbles to strikes.
The fighters who do the best against him are kickboxers who can utilize their knees and legs effectively to outrange him and KO him or take him to decisions, like Anderson Silva and Overeem. Wrestlers usually don't do that well against him because he has great TD defense and even if you get him there he has nasty jiu-jitsu. Remember that Vitor is a black belt under Carlson Gracie, and that actually means something unlike being a BJJ black belt under the Nogueira brothers.
Sonnen would have a hard time getting Vitor down and unlike with Anderson, I don't think Sonnen would be able to simply eat through Vitor's devastating jabs to get the TD. He would likely get KOd if he tried to do that. Anderson is a more talented striker than Vitor, but he does not have the devastating power with his fists that Vitor has. If Sonnnen takes Vitor down, he has to deal with a guy who has almost Werdum-like level of BJJ, and we all know that Sonnen's submission defenses are terrible.
Conclusion: Vitor wins by KO or TKO in the first round, or by submission in the second or third round.
Fair break down of the fight, but i'd still give an edge to Chael just because of how tough and hard to beat he is. You are right about Vitor being the most dangerous fighter on the planet in the first round though, he is really that good. Theres an interview Sonnen did where he talks about how good Vitor really is and how he has trouble putting it all together sometimes, he sounds like he has a HUGE amount of respect for Belfort and what hes done in the last 15 years.