The Nationals have entered a full rebuild less than two years after winning the World Series, also trading away Max Scherzer, Trea Turner, Kyle Schwarber, Brad Hand, Daniel Hudson, Yan Gomes and Josh Harrison in a 24-hour span.
The 37-year-old Lester was 3-5 with a 5.02 ERA in 16 starts during his first season with Washington. He has won three World Series titles in his 16-year career: two with Boston and one with the Chicago Cubs.
The Cardinals entered Friday at .500 and trailing first-place Milwaukee by 9 1/2 games in the NL Central. St. Louis was 7 1/2 games behind in the NL wild-card race.
“The sense of urgency is still as high as it was beginning of April, the middle of May,” Cardinals manager Mike Shildt said.
Washington acquired speedy 25-year-old outfielder Lane Thomas from St. Louis. Thomas hit .104 in 32 games for the Cardinals this season.
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