Swanson capped a five-run first inning with his three-run shot. Reese McGuire, Nico Hoerner and Ian Happ hit solo home runs and the Cubs never trailed in winning for the fifth time in seven games.

Luis Garcia Jr. hit a two-run home run and Daylen Lile added two RBI and a pair of triples for the Nationals, who had their three-game winning streak halted.

Chicago's Javier Assad (2-1) won his second straight start, working the first 5 1/3 innings. He gave up the Nationals' first four runs on three hits and two walks with four strikeouts.

Jake Irvin (8-11) dropped his fourth straight start after allowing Chicago's first seven runs in 3 1/3 innings. He allowed five hits and walked four with two strikeouts.

After Pete-Crow Armstrong's sacrifice fly and Hoerner's RBI double, Swanson went deep to give the Cubs a big early lead. McGuire added a solo homer off Irvin in the second and Hoerner added one of his own off Shinnosuke Ogasawara in the sixth. Happ closed the scoring with a solo homer off Konnor Pilkington in the eighth.

Assad didn't allow a hit until the fourth, when Lile got on with a two-out triple before scoring on Garcia's 12th homer of the season.

Chicago outfielder Kyle Tucker missed his second straight game with a calf injury. The club hopes to get him back in the lineup - possibly at DH - this weekend. He left Tuesday's win over Atlanta with the injury.

Key moment

Swanson got a big roar from the school-/work-day crowd of 32,320 when he hit Irvin's first-inning offering deep into the left-center bleachers.

Key stat

Crow-Armstrong had an efficient day at the plate with two singles, a run, a stolen base and two RBI.