Frankie Edgar wasn't ready to give up his spot on this list. At UFC 118 in Boston, he fought every bit like a man who belonged on it.
For the second time in four months, "The Answer" got a unanimous decision nod over B.J. Penn. This time around, there wasn't a shred of controversy, as Edgar dominated Penn for 25 minutes and affirmed his place here. In maybe MMA's most talented division, he'll have the chance to really add to that résumé in the future with a stream of top-notch 155-pounders in his sights, including his first challenger -- the only man to defeat him -- Gray Maynard.
With his loss, Penn exits this list, on which he's enjoyed a spot since March 2008. However, stepping back into the fold is one of Penn's lightweight coevals.
Gilbert Melendez staked his claim as one of the sport's best back in April, smashing on Dream lightweight champ Shinya Aoki in a hugely significant lightweight bout. That win, combined with Penn's loss, allow Melendez to slip back into the pound-for-pound top 10. Melendez previously enjoyed real estate here from the initial Sherdog pound-for-pound list in September 2007 up to his June 2008 loss to Josh Thomson.