When predicting the outcome of UFC 155's headliner, it's a matter of what you discount.

Junior Dos Santos (15-1 MMA, 9-0 UFC) and Cain Velasquez (10-1 MMA, 8-1 UFC) fought for 64 seconds – almost no time to gather new information on the style matchup – when they first met 13 months ago at UFC on FOX 1.

Prior to the bout, UFC brass floated two possible scenarios: a quick blowout or a five-round grinder. The former came true: Dos Santos clubbed then-champion Velasquez with an overhand right, and a few seconds later, he was the new heavyweight titleholder.

So there isn't a tremendous amount of context to add to what was already there when breaking down the rematch, which headlines UFC 155 on Saturday at MGM Grand Garden Arena in Las Vegas. (Main-card fights air on pay-per-view following prelims on FX and Facebook.) But that doesn't stop observers from trying.

Recently, a video has circulated revealing a previously rumored knee injury Velasquez suffered before the first fight. Some have hinted that he may have been pressured into taking the bout given the monumental importance of the UFC's network-TV debut.

Velasquez has discounted his ailment's importance, and Dos Santos, who suffered his own knee injury prior to the bout, has taken umbrage to the implication that favorable circumstances led to his win.

But it's about all there is to add to pot. Dos Santos appears more muscular prior to the fight. Other than that, the happy-go-lucky champ and his quieter counterpart remain much the same by appearances. Only the fighters and their trainers know what's really different, if anything, the second time around.

Both heavyweights have fought once since their first fight, and each encountered little resistance on the way to victory. Dos Santos beat up an overmatched Frank Mir, and Velasquez mauled Antonio Silva. Neither was really tested in areas in which he might be weaker (the champ on the mat and the ex-champ standing).

So you can give credit to Dos Santos for quickly dismantling Velasquez. You can discount it as the result of Velasquez's knee. You can fault the ex-champ for a bad game plan, or the current one for a good one. Or, you can go back to the original prediction: that the bout will either be very short or very long.

Then there's the virtual certainty that preconceived notions of how the fight will turn out will be turned on their head in some way.

Velasquez is still a great ground-and-pound artist and has more impressive mat credentials than Dos Santos, who recently claimed his jiu-jitsu black belt. But this isn't a wrestling match. And Dos Santos is still a great boxer who's knocked out most of his competition. But this isn't a pure boxing match. Against each other, they have sizable obstacles to using their most effective weapons.

What sets them apart is that Dos Santos already has proven his ability to surmount those obstacles. It could take him longer the second time around since Velasquez won't want to expose himself to the same fate. Then, it's the time honored tradition of who is more effective and who makes the first mistake.

Betting lines favor Dos Santos' fists over Velasquez's, and he's a 2-to-1 favorite. Velasquez was a slight favorite the first time around. So that punch has shifted perceptions, but not by much. The matchup is still a close call.

Other main-card fights

Joe Lauzon (22-7 MMA, 9-4 UFC) vs. Jim Miller (21-4 MMA, 10-3 UFC): Lightweight bonus-machine Lauzon hopes to tie middleweight champ Anderson Silva's mark of 12 fight-night bonus checks when he meets the grinding aggression of Miller, who hopes to rebound after failing to stop the rise of Nate Diaz. Lauzon, who earlier this year couldn't check possible contender Anthony Pettis, could take the next spot in line if Pettis beats Donald Cerrone next month at UFC on FOX 6. But he's got to contend with the technical mastery of Miller, who shuts down all but the top fighters with a grappling-heavy attack. Scrambles are where Lauzon excels, and that's where he might prevail. If Miller is ready, though, it could be a long night for both.

Tim Boetsch (16-4 MMA, 7-3 UFC) vs. Costa Philippou (10-2 MMA, 4-1 UFC): A bout with middleweight title implications got a downgrade when Boetsch's original opponent, Chris Weidman, was forced from the matchup with an injury. That leaves Philippou, who's won his past four, in the spoiler role. Boetsch has better victims on his resume and has a lot to lose against his hard-punching opponent. But while Philippou has shown improvement in areas not related to his primary discipline (boxing), he may not be at the level of Boetsch when it comes to the clinch and ground game. Betting lines have them even, which is perhaps a commentary on Boetsch's lackluster performance against Hector Lombard, but people may be in for a surprise when they match power.

Yushin Okami (27-7 MMA, 11-4 UFC) vs. Alan Belcher (18-6 MMA, 9-4 UFC): Another dead heat characterizes this middleweight bout, which favors Belcher in career outlook if he wins. Okami already has been to the top of the mountain, and after a title loss to Anderson Silva, he fell short to Boetsch before rebounding against the unheralded Buddy Roberts. Belcher, meanwhile, took out leg-breaker Rousimar Palhares, and before that, he took out a tough trio of Jason MacDonald, Patrick Cote and Wilson Gouveia, so it's unclear why things are so even to gamblers. Perhaps it's Okami's ability to use his size to muscle his opponents in close and on the mat. It can't be he striking, which Belcher equals (or comes out better) in a side-to-side comparison. And it shouldn't be Okami's previous win over Belcher, which happened six years ago in the infancy of Belcher's development. Whatever the case, Okami is more cold than hot these days and may not be able to match his fast-improving opponent.

Chris Leben (22-8 MMA, 12-7 UFC) vs. Derek Brunson (9-2 MMA, 0-0 UFC): An ill-fated trip to "The Ultimate Fighter 17" tryouts has turned into a short-notice opportunity for middleweight Brunson, who's lost two straight coming into his octagon debut. Scant preparation time did him no favors in his most recent bout, a 41-second KO loss to ex-Strikeforce champ Ronaldo "Jacare" Souza. But in Leben, he gets a more predictable challenge. The longtime veteran and reformed wildman, who's sat on the bench a year following a second suspension for banned substances, is a heavy puncher with good skills in the clinch and a rock-hard head. As long as Brunson can avoid big bombs, he should have the advantage in speed and power, and he's got the advantage of being more active as of late. Leben, however, can never be counted out due to his never-say-knockout spirit.

UFC 155's full card includes:

MAIN CARD (Pay-per-view, 10 p.m. ET)
Champ Junior Dos Santos vs. Cain Velasquez - for heavyweight title
Joe Lauzon vs. Jim Miller
Tim Boetsch vs. Constantinos Philippou
Alan Belcher vs. Yushin Okami
Derek Brunson vs. Chris Leben
PRELIMINARY CARD (FX, 8 p.m. ET)
Brad Pickett vs. Eddie Wineland
Byron Bloodworth vs. Erik Perez
Melvin Guillard vs. Jamie Varner
Myles Jury vs. Michael Johnson
PRELIMINARY CARD (Facebook, 6:30 p.m. ET)
Philip De Fries vs. Todd Duffee
Leonard Garcia vs. Max Holloway
Chris Cariaso vs. John Moraga