Starlin Castro hit a run-scoring double in the eighth inning to break a scoreless tie and Aramis Ramirez hit a two-run homer to lift the Chicago Cubs to a 4-0 win over the Washington Nationals on Wednesday night.

Ryan Dempster (12-8) threw seven scoreless innings, allowing two hits and striking out eight.

Washington's Jason Marquis (0-7) remained winless this season despite his best pitching performance of the year. He gave up one run on four hits in 7 1-3 innings, walking three and striking out two.

Alfonso Soriano led off the ninth inning with a home run to left-center field, his 21st homer of the season.

Chicago improved to 3-0 under interim manager Mike Quade, who took over when Lou Piniella unexpectedly retired after Sunday's game. Quade is the first Cubs manager to win his first three games since Jim Riggleman, now the Nationals' skipper, started 4-0 in 1995.

Entering the game Dempster hadn't lost any of his four starts in the month of August, and Marquis had lost each of his six starts this season.

The two right-handers didn't allow any offense for the first seven innings before a leadoff walk in the eighth to Tyler Colvin, pinch-hitting for Dempster.

Marquis was relieved by Tyler Clippard with one out in the inning and Colvin on first base. Colvin quickly stole second and was doubled home by Castro to leave Marquis on the hook for the loss.

Marquis was making his fourth start since returning from a nearly four-month stint on the disabled list and having surgery to remove bone chips from his elbow and he ended up with by far his best performance of the year. It was the first time this season Marquis had pitched more than five innings. He lowered his ERA from 11.39 to 8.79.

Dempster has now won four of his five starts this month. He had a no decision in his last outing against Atlanta on Friday, giving up two runs on four hits in eight innings.

Ramirez game the Cubs a 3-0 cushion with his two-out home run to left field in the eighth, scoring Castro. It was Ramirez's 20th homer of the season.

Marquis became the game's first base runner to reach third base in the sixth inning. He singled, advanced on a sacrifice and moved to third on a wild pitch with two outs but was stranded when Ian Desmond grounded out to end the inning.

NOTES: Nationals RHP Stephen Strasburg, on the DL with a right strained forearm tendon, will have a second MRI Thursday to determine the extent of the injury. His scheduled spot in the rotation Thursday will be filled by RHP Jordan Zimmermann. Zimmermann has not pitched in the majors since undergoing Tommy John surgery last August. ... OF Nyjer Morgan was suspended seven games for hitting a fan with a ball thrown into the stands at Philadelphia Saturday. Morgan appealed the suspension and played Wednesday. ... OF Josh Willingham had left knee surgery Wednesday and is unlikely to play again this season. ... According to STATS LLC., Soriano is one of five players to have at least 20 home runs in each of the nine seasons. The others are Alex Rodriguez, Albert Pujols, Adam Dunn and David Ortiz.