Tuesday night in Houston, the quarterfinal round of the CONCACAF Champions League kicks off with MLSs Houston Dynamo hosting Atlante of Mexico.
The top-level club competition in the region brought about a few surprises in the group stage, notably the advancement of two USL teams, Montreal and Puerto Rico, and there are sure to be more unexpected outcomes going forward.
With that in mind, heres a look at some of the developing storylines heading into the final eight, and how they might determine who struts away with a trophy and shuffles back home. 
Injury Problems For Marathon
Marathon will take on the Puerto Rico Islanders with a host of injuries hampering the squad. No less than eight players from the Honduran side are battling for fitness, including midfielder Maynor Suazo, defender Erick Norales, and defender Mario Beata.
Suazo, the cousin of Benfica star David Suazo, is a supremely gifted midfielder. Norales proved in the group stage that he is not only a rugged defender, but has a nose for goal. The 34-year-old Beata is a proven commodity who provides the Green Monsters with a calming presence at the back.
The loss of such key players could prove to be the downfall of the heavily favored Hondurans. The scrappy Islanders this winter bolstered their attack with the acquisitions of Jamaican striker Nicolas Addlery and Uruguayan midfielder Martin Nunez, a rookie sensation in 2008 with the Carolina Railhawks.
USL Hits The International Stage
The biggest storyline of the CCL has been the fantastic run from two USL teams. But can either Cinderella advance to the semifinals, or will the slippers fall off?
Both the Montreal Impact and the Puerto Rico Islanders benefited in the group stages from playing against reserve squads from the bigger clubs who were in season and resting players.
Now, the USL is out of season, meaning that Montreal and PR are in preseason form rather than the midseason highs on which they rode through the group stage. The upside is that neither is facing a team that has been particularly stellar of late.
Montreal face Santos Laguna, who are struggling to find their legs early in the Mexican Clausura season, having won only once in their first six matches. They sit in last place in the Primeras Group 1, and could be without prolific marksman Chucho Benitez, who injured his shoulder in early February. The defensive-minded Canadians allowed only five goals in six group matches. If they can continue their defensive ways, they could prove to be a tough test for a Mexican squad without its top striker.
As mentioned above, Marathon will come into the tie with Puerto Rico nursing plenty of injuries. The Islanders will need to take advantage of the Hondurans defensive woes to advance. However, Collin Clarks squad proved to be very opportunistic during the group stage, advancing despite a -1 goal differential. If Marathon waver at the back, look for the USL runners-up to take full advantage.
That said, the odds are still heavily stacked against either USL team reaching the semifinals.
MLSs Lone Hope
Houstons tie with Atlante is full of intrigue. Gone from the Dynamo are forward Nate Jaqua (Seattle) and midfield maestro Dwayne De Rosario (Toronto). Both figured prominently in Houstons advancing from the group stage.
But plenty of firepower should still be on display for the Dynamo. US international mainstay Brian Ching leads the attack, with highly touted midfielder Stuart Holden filling the void left by De Ros departure.
Atlante can match Houstons arsenal, though. Venezuelan striker Giancarlo Maldonado is an accomplished goal scorer, and attack minded Christian Bermudez keys the attack.
The match will be Houstons first competitive action since clinching a spot in the quarterfinals back in November. Atlante began league play in January, although they have only one win so far in the Clausura season.
The last meeting between the two sides in international competition came during the 2008 SuperLiga, where Houston routed the Iron Colts 4-0. That match saw an on-form Houston side playing against an out-of-season Atlante. With the tables turned for the CCL, it will be interesting to see if Houston can duplicate the result and push onto the semifinals.
The Quarterfinal Derby
The UNAM Pumas-Cruz Azul match will feature the first-ever derby in the CCL knockout stages.
The two teams squared off in last falls quarterfinals of the Mexican Apertura with the Azulinos notching a 3-1 victory.
But Pumas have been the class of the CCL to this point. Pumas roll into the quarterfinals not only as the sole undefeated side in the tournament, but also as the leading scorers of the group stage, having tallied 18 goals in six matches.
Cruz Azul struggled through Group A, finishing in second on goal differential over Deportivo Saprissa of Costa Rica.
Pumas currently sit just one point ahead of Cruz Azul in the Mexican Premier League, Group 2 standings.