Yes. The Cowboys have swept the home-and-away series with Washington 16 times, most recently during the 2011 season.
Yes, many times...in 1968, 1969, 1970, 1977, 1980, 1981, 1985, 1994, 1998, 1999, 2000, 2001, 2003, 2004, 2009 and 2011.
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Redskins
The Dallas Cowboys' first season in the NFL was 1950.
Twice, as his Dallas Cowboys swept Lombardi's Washington Redskins in the 1969 season. They were Landry's only career wins over Lombardi in seven games counting Lombardi's tenures with the Packers and Redskins.
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Frankly, the Dallas Cowboys have dominated their series with Washington for the past 15 years or so. But Washington has acted as a spoiler several times.
Redskins
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