"Walking him three times, I think that really kind of hurt," said Hamels, who allowed three earned runs over 5 2/3 innings in a no-decision. "For a lefty-lefty matchup, you have to attack him. No matter what type of dangers and what he's obviously capable of doing. You have to try to get him out.
After turning those three free passes into one run scored, Harper clobbered a cutter from Wilson in his fourth plate appearance, a shot to dead center that traveled a projected 413 feet, according to Statcast™, to give the Nationals their first lead of the game in the seventh inning. It was his 32nd homer of the season.
In the process, Wilson's scoreless-outings streak was snapped at 14, and the Cubs' lead over the Brewers atop the NL Central dwindled to 2 1/2 games. It's their smallest margin since a victory over the Tigers on Aug. 22.
"We had the right pitchers lined up, they were rested, and they got us," manager Joe Maddon said. "They absolutely got us. There's no complaining on our side. We normally get that game done."
Chicago gave back a four-run lead in a nightcap that ended at roughly 12:45 a.m. CT after a delay of 1 hour, 29 minutes following the top of the eighth. After Friday's washout, Saturday's first game was also plagued by a delay of 2 hours, 10 minutes prior to first pitch.
Hamels' three runs allowed were his most in eight starts since being acquired in a trade with the Rangers. They all came after rookie Victor Caratini's first career grand slam -- and third career home run -- staked Chicago to a 4-0 lead in the fourth inning off Nationals starter Jefry Rodriguez.
Hamels allowed an RBI triple and RBI double to Adrian Sanchez, a second-year player who hadn't played in a big league game since June before starting both games of Saturday's doubleheader.
"No matter who they are and what type of track record they have, you have to be able to execute," said Hamels, who allowed only three hits but issued five walks. "And I didn't execute multiple times to him."
The Cubs still appeared to be heading for a split of the twin bill when Kris Bryant's seventh-inning double off Wander Suero scored Terrance Gore from third to make it 5-3.
Steve Cishek came on in the bottom half and gave up an RBI double to Anthony Rendon, prompting Maddon to turn to Wilson to face the left-handed-hitting Harper. After working a 1-1 count, Harper connected for the decisive blow.
"Any pitch properly thrown in the right spot is always the right pitch," Maddon said. "He just didn't get it in the right spot."
YOU GOTTA SEE THIS After sitting out the opener, shortstop Javier Baez made an immediate impression in Game 2, tracking Trea Turner's foul pop to the warning track before making a slick, back-handed grab just a step from the railing to record the Cubs' first out of the game.
GORE ON TO SCORE After Tommy La Stella led off the seventh with a pinch-hit single, Gore entered as a pinch-runner with one out and immediately created havoc on the basepaths. He swiped second despite an awkward late slide, when Nats shortstop Turner might've caught him skidding past the base had he held the tag. Then, Gore took third more comfortably for his fourth steal of the season as Albert Almora Jr. struck out for the second out of the inning. The twin thefts came after the 27-year-old speed merchant registered his first career hit against Scherzer in Game 1.
SOUND SMART The Cubs were swept in a doubleheader for the first time this season after splitting three previous twin bills, which were all of the day-night variety. The twin bill also appears to be the franchise's first played in Washington in more than 121 years. On Aug. 20, 1897, the Chicago Colts split a pair of games with the Washington Senators at Boundary Field.
UP NEXT The Cubs conclude a season-long 11-game road trip at 12:35 p.m. CT on Sunday as left-hander Mike Montgomery (4-5, 3.85 ERA) will start the series finale at Nationals Park. Montgomery is coming off back-to-back starts of fewer than five complete innings after returning from the disabled list (shoulder inflammation) on Aug. 30. Righty Erick Fedde (1-3, 6.00) starts for the Nats.
Ian Quillen is a contributor to MLB.com based in Washington.