Three bad pitches suddenly spoiled an otherwise solid outing for Jordan Zimmermann.

The Washington starter gave up three runs in the seventh inning and the Chicago Cubs went on to beat the Nationals 4-3 Thursday.

Chicago broke a 1-all when Reed Johnson reached on a two-out single and Aramis Ramirez and Carlos Pena hit consecutive home runs.

"I had two strikes on Johnson and threw a fastball and he got a base hit and threw a halfway decent slider to Ramirez," Zimmermann said. "The pitch to Pena was the first changeup of the day and probably the worst choice I made all day."

Ramirez's two-run shot was his 21st of the season and gave him 16 homers since June 25, the most in the major leagues since then.

Pena followed with a drive that curled around the pole in right field and landed on Sheffield Avenue.

Until that point, Zimmermann (7-10) had scattered six hits, struck out seven and walked just two, including one intentionally.

I felt great, fastball command was there, I had a good curveball and a good slider today," he said. "It was just three pitches ... and that kind of ended my day."

A half-inning earlier, Washington first baseman Mike Morse left the game when was hit in the left arm by Cubs starter Ryan Dempster to lead off the inning. Morse was X-rayed and examined at a hospital.

"His whole arm was shaking," Nationals manager Davey Johnson said. "I thought it was the funny bone, but it must of hit more than the funny bone because the muscles in his arm were reacting kind of erratically."

Dempster (10-8) limited Washington to a first-inning home run by Ryan Zimmerman and went seven innings, allowing three hits, walking two and striking out six.

Zimmerman homered onto Waveland Avenue beyond the left-field bleachers to extend his hitting streak to 19 games, the second-longest active streak in the big leagues behind the 31-game streak of Atlanta's Dan Uggla.

Washington loaded the bases and scored a run in the ninth against Carlos Marmol, but he recovered to get his 26th save.

Wilson Ramos hit a high chopper off Marmol that he beat out for an infield single, scoring Jonny Gomes. But Marmol struck out Brian Bixler and got Rick Ankiel on a fly ball to the wall in center to end the game.

Marmol has converted seven straight saves since returning to closer's role on July 31. Washington also scored a run in the eighth, when pinch-hitter Bixler hit an infield single.

Ankiel followed with a single, but Cubs reliever Kerry Wood struck out Danny Espinosa and Zimmerman.

Wood has struck out the last eight batters he's faced, matching a Cubs mark for the most since big league mounds were lowered in 1969.

Zimmermann reached 145 innings for the season, leaving him two or three starts left before he gets to his limit of 160 for the season. He had Tommy John surgery nearly two years ago.

"He still had a real low pitch count and I wanted to get him the win," Johnson said.

NOTES: Livan Hernandez will start the opener for Washington against Philadelphia's Cole Hamels. Hernandez hasn't won at Citizens Bank Park since May 31, 2006. ... Despite an announced crowd of 34,733, just about half the seats were actually occupied on a picturesque afternoon at Wrigley Field. Thursday's game was a makeup of Monday's rainout.