CHICAGO -- The Chicago Cubs keep hitting home runs.
Ramirez's two-run shot in the seventh was his 21st of the season, and gave him 16 homers since June 25, the most in the major leagues since then.
"However we can score," Cubs manager Mike Quade said. "The guys are hitting the ball out of the ballpark and that's a good thing."
Pena followed Ramirez with a clout that curled around the pole in right field and landed on Sheffield Avenue and put the Cubs up 4-1.
"You like to be able to create any way you can, but the long ball is still a part of it," Quade said.
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.
"Marm gutted it out," Quade said. "That was something. I'm out of breath."
Marmol has converted seven straight saves since returning to the closer's role on July 31. He was pitching for the third straight day, too.
"When you ask a guy to come out for a third day, you're always worried," Quade said. "He's done it before. He just wasn't as sharp command-wise.
"He could have collapsed at any time there and didn't. Got back in the strike zone when he needed to. Just a gutsy performance on a day when he didn't have his (best) stuff."
Wood has struck out the past eight batters he's faced, tying the Cubs' record for all pitchers since the mounds were lowered in 1969.
Washington starter Jordan Zimmermann (7-10) allowed four runs and nine hits in 6 2/3 innings. He walked two and struck out seven.
The Cubs have won nine of their past 11 games and got their third straight series win at home, something they hadn't done since 2009.
"It was a fun day for us," Dempster said. "It was a good way to end a homestand."
Zimmermann held the Cubs to one run on six hits through six innings but ran into trouble after striking out the first two batters of the seventh. Johnson laced his third single of the game into left field. Ramirez followed with a shot into the left-field bleachers, putting the Cubs up 3-1 before Pena's homer chased Zimmermann.
"Threw a halfway decent slider to Ramirez but he was sitting on it and it doesn't take much to hit it out of here," Zimmermann said. "He got the bat on it, got it up and it was a home run.
"And then the pitch to Pena was the first changeup of the day and probably the worst choice I made all day. I don't really know why I threw it."
Dempster won his third straight start and reached 10 wins for the fourth straight season. He's won 10 or more seven times in career. Only Fergie Jenkins (15) and Reggie Cleveland (8) have more 10-win seasons among Canadian-born pitchers.
Zimmerman opened the scoring in the first when he 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.
Chicago tied it in the fourth on Soriano's RBI triple. Right fielder Jayson Werth dove for the ball but it clipped the end of this glove and rolled to the wall. Byrd scored and Soriano wound up at third with his first triple since Aug. 23 of last season.
Zimmermann reached 145 innings for the season, leaving him two or three remaining starts before he reaches his limit of 160 for the season. He had Tommy John surgery nearly two years ago.
Washington's Michael Morse had to leave the game after being hit on the elbow by a pitch. He went to the hospital and manager Davey Johnson said he wasn't sure if Morse would be able to make the team's flight to Philadelphia, where the Nationals begin a three-game series on Friday. "We've got to keep our fingers crossed," Johnson said. "Yeah, I'm worried because he's got huge arms and that'll protect it, but he's in bad shape."... After the game, the Cubs' ground crew began resodding sections of the Wrigley Field turf that were damaged during a pair of recent concerts given at the ballpark by former Beatle Paul McCartney. Byrd recently complained about the surface after a game in which he lost his footing... Cubs starter Andrew Cashner completed a bullpen session before Thursday's game with no problems, the latest step in his recovery from a strained right rotator cuff. The Cubs travel to Atlanta for a three-game weekend series against the Braves, the first leg of a six-game road trip that will also stop in Houston. Carlos Zambrano is set to face Atlanta's Mike Minor on Friday. Zambrano has hit 23 career HRs. He tied Walter Johnson for ninth among pitchers with his homer off Johnny Cueto on Aug. 6. Zambrano is 0-4 with a 6.24 ERA in past 10 starts against Atlanta since July 13, 2003. . The Nationals' Livan Hernandez will start the opener for Washington against Philadelphia's Cole Hamels.