When Anthony Pettis first fought Ben Henderson at WEC 53, he opened as a +155 underdog and closed as high as +220. Twenty-five enthralling minutes plus one "Showtime kick" later, Pettis emerged as the WEC's final lightweight champion and he remains the only man to defeat Henderson under the Zuffa banner. Through several twists and turns that would take too long to explain here, Henderson has gone 7-0 since the Pettis loss and is the reigning and defending UFC champion, while Pettis' title shot came through T.J. Grant's injury.
Nevertheless, this is a rematch that many fans have been eager to see, and while Bendo opened as the small favorite over Pettis (-160/+120), the up-to-date odds have Pettis with the edge: (via BestFightOdds)
It didn't take long for the lines to change and for money to come in on Pettis. I tend to think that Henderson opening as the favorite is partially related to the status of Pettis' torn meniscus, which was supposed to keep him out of a potential UFC 164 date (against any opponent) but is apparently not severe enough anymore to deny him the Henderson fight.
For the record, Henderson opened as a -265 favorite over T.J. Grant.