Aspelin and Knowle earlier in the tournament ousted the world No. 1 doubles team of Bob and Mike Bryan in straight sets.
They claimed the championship with a 7-5, 6-4 victory over Lukas Dlouhy and Pavel Vizner, the No. 9 seeded doubles team. Aspelin and Knowle dropped their service game just once in the match, closing out Dlouhy and Vizner in 84 minutes.
The U.S. Open doubles championship is worth $400,000 to Aspelin and Knowle while Dlouhy and Vizner will split $200,000.