Yadier Molina's (two-run single in the fifth inning put the Cardinals on top to stayin a 4-1 win over Washington.
Molina's hit made a loser of Washington starter Jordan Zimmermann who failed in his bid to become a 20-game winner this season.
Cardinals rookie Shelby Miller notched his 15th win of the season.
Matt Adams homered for the NL Central leading Cardinals who took another step closer to wrapping up the division title. The Pirates' hopes of catching up in the NL Central took a big hit when Darnell McDonald launched a three-run homer, leading the Chicago Cubs to a 4-2 win.
Trailing by those three games in the division, both the Cards and Pirates have three games remaining in the regular season.
The Pirates, who already have clinched a playoff spot, hold a one-game lead over Cincinnati for the first wild-card slot. Pittsburgh and the Reds finish up with a three-game set in Cincinnati this weekend.