Starlin Castro had two RBIs and Anthony Rizzo went 3 for 4 with two doubles and a run scored.
The Cubs had dropped four of five games before the win.
Denard Span went 2 for 4 with two doubles and two RBIs for the Nationals.
Neither starter was involved in the decision. The Cubs' Travis Wood gave up three runs on seven hits in 6 2/3 innings and was hurt most by five walks. Washington's Doug Fister also allowed three runs on seven hits.
Cubs reliever Neil Ramirez (1-1) got the win and Hector Rondon pitched a perfect ninth for his ninth save.
Cubs center fielder Junior Lake had to leave in the second inning after crashing into a door in the outside wall at Wrigley Field chasing a drive by Ryan Zimmerman. The wall is not covered with ivy. The Cubs said Lake has shown no signs of a concussion and has some bruises, including one on his head.
The Cubs opened the scoring with three runs in the fourth by bunching hits. Ruggiano's lead-off grounder surprisingly was scored a hit when third baseman Anthony Rendon threw well wide of first.
Rizzo followed with a double. Castro, who took over the team lead in RBIs on Wednesday, added to his total with a two-run single. One out later, Welington Castillo singled to drive in Castro.
Washington finally pushed across a run in the sixth. Span led off with a double and Rendon immediately drove him in with a single.
It appeared the lead was about to shrink further after Wood walked Jayson Werth. But Wood got Adam LaRoche to ground into a double play. Following another walk, he struck out Ian Desmond to end the inning.
Wood wouldn't be so fortunate in the seventh. He started the inning with back-to-back walks and, following a sacrifice bunt, two runs scored on a double by Span to tie the score at 3.
The Cubs staged their rally in the bottom of the inning and took the 5-3 lead on Ruggiano's double off reliever Craig Stammen (0-3).
NOTES: Nats OF Bryce Harper (torn ligament left thumb) is on a rehab assignment at Double A Harrisburg and could be activated Monday if all goes well. ''When he comes back we want him to feel good at the plate, feel good in the field and have his legs underneath him full go,'' manager Matt Williams said. ''We don't know how the next three or four days will go, but he's well on his way.'' . Cubs manager Rick Renteria said he won't start catcher Castillo (rib cage inflammation) every day initially now that he's back from the DL. ... The Nats activated C Wilson Ramos (strained right hamstring). . RHP Tanner Roark (7-4) faces Jason Hammel (6-5) in the second game of the four-game series.