Detroit's late fireworks were preceded by early ones from Harper.
The reigning National League Most Valuable Player hit his first two Grapefruit League home runs, taking Verlander deep for a two-run shot in the top of the first inning and a solo blast in the fifth.
"One was a breaking ball that was up and middle, and the fastball up and away -- which I know he loves the ball there," Verlander said. "Just gotta execute it better."
Verlander entered Sunday having thrown nine scoreless innings over three appearances. He was solid outside of dealing with Harper, scattering six hits, striking out two and walking none.
Nationals starter Joe Ross exited the game in the top of the second after getting hit on the right heel by a Nick Castellanos comebacker. Ross was diagnosed with a bruised right heel and will be reevaluated Monday.
Blake Treinen came on in relief and threw four scoreless innings, allowing two hits and fanning three.
Up next for the Nationals: They return to Space Coast Stadium and play the Astros at 1:05 p.m. ET, and the game will air on Gameday Audio. It marks the fifth time the two teams will face each other. The Nationals have the series lead at 2-1-1. Left-hander Gio Gonzalez will make the start for Washington, his first since March 15 as he was away from camp for the birth of his son. In his last start against the Astros, Gonzalez pitched four innings, allowed a run on three hits and struck out four batters.
Up next for the Tigers: Anibal Sanchez is scheduled to make his first start of the spring at 1:05 p.m. ET on Monday against the Phillies at Joker Marchant Stadium, and fans can listen to the action on Gameday Audio. The right-hander is recovering from triceps inflammation, and he likely won't throw much more than three innings or 45 pitches.
Cash Kruth is a reporter for MLB.com. Follow him on Twitter at @cashkruth. This story was not subject to the approval of Major League Baseball or its clubs.