A quartet of compelling second legs pared the MLS playoff field down to four in midweek. The remaining sides – D.C. United and Houston in the East and Los Angeles and Seattle out West – all harbor realistic ambitions of emerging victorious in the final on Dec. 1.
 

First leg: Sunday at BBVA Compass Stadium, Houston
Second leg: next Sunday at RFK Stadium, Washington, D.C.

Look for a physical and tight affair between two sides that will approach this series in fairly conservative fashion. Houston might enter the tie as slight favorites after dispatching top-seeded Sporting Kansas City and engineering a similar run to reach the final last year, but United can point to its recent momentum and its gritty 1-0 victory over New York on Thursday night to suggest a berth in MLS Cup remains firmly on the table.
 

United has ticked along pretty nicely without its best player over the past two months (6-0-3 since De Rosario suffered a knee injury). But if De Rosario is healthy, he offers a dynamic dimension that might be required to unlock a Dynamo outfit that won't give much away over these two legs. Integrating him back into the side could be a problem, but it is a sacrifice worth making for one of the top two or three postseason performers in MLS history.

Both of the Dynamo's attacking strengths – set pieces and wide play – hinge on Davis' ability to provide quality service from the left. His postseason pedigree suggests he will find a way to influence one or both of these matches by offering the delivery to fuel the Dynamo's robust attack.

First leg: Sunday at the Home Depot Center, Carson, Calif.
Second leg: next Sunday at CenturyLink Field, Seattle

A daunting task awaits the Sounders in their first trip to this stage of the postseason. The defending champions discovered their form at the right time and swept aside Supporters' Shield winners San Jose 3-1 in midweek to continue their title defense. Seattle must lean on its stingy rearguard to ward off a Galaxy side that looks primed to continue its second-half run.
 

Michael Gspurning and Jeff Parke must continue their defensive work in order for the Sounders to compete, but the difference between winning and losing could come down to the health of Rosales. The veteran Argentine schemer missed the second leg victory at Real Salt Lake with a hamstring injury. If he isn't fit enough to feature (and Seattle boss Sigi Schmid hinted at a second leg return after the win at RSL on Thursday night), then the Sounders would struggle to conjure up the necessary creativity in the final third.

The Ireland captain leads a potent Galaxy attack capable of ripping even the resolute Sounders apart. His movement and his predatory instincts (including a pair of goals at Buck Shaw Stadium on Wednesday night) dovetail nicely with Edson Buddle's target play and Landon Donovan's incisive running. If he continues in his currently rich vein of form, then the Galaxy will likely secure yet another MLS Cup appearance.