Sporting managed a 1-0 extra-time win over Houston Dynamo Aggie Soccer Stadium in College Station, Texas thanks to a goal from CJ Sapong in the second minute of the first overtime period.
In Maryland, DC edged Philadelphia Union 4-2 on penalties after extra-time finished 2-2. The Union struck first in the 18th minute through Carlos Ruiz before United hit back just before half-time through Josh Wolff.
There were no further goals until extra-time when DC defender Daniel Woolard smashed home before Philadelphia's Brian Carroll with two minutes remaining to force penalties which DC saluted 4-2 thanks to a vital save by keeper Bill Hamid.
Both winning teams are now two of seven remaining MLS clubs vying for the two play-in berths available for the U.S. Soccer national club tournament.