The 24-year-old right-hander was hit in the fleshy part of his hand, just below his glove. The play happened in the fourth inning.
"I thought I could have caught it," Strasburg said. "It just took a while for it to sink in that it hit me. It kind of got numb. I just shook it out and it was just tender after that."
After shaking off the injury and being cleared by team trainers, he struck out two of the next three batters.
Manager Davey Johnson said he was just glad it was Strasburg's glove hand that was hit. He also said Strasburg did not have to talk him into letting him stay in the game after he was examined by a team trainer.
"It was a scare, no doubt about it," Johnson said.
Strasburg, making his sixth spring start, gave up three runs and seven hits. He struck out five and walked one.
"I thought I pitched pretty well," Strasburg said. "I got weak contact, it was just the story of (the game). They singled me to death besides that home run early. That's baseball."
After letting Strasburg throw 89 pitches against Detroit, Johnson said he likely will limit him to around 70 in his final spring start on Wednesday so he doesn't overwork him before the start of the season.
Strasburg, meanwhile, is ready to go.
"I think my arm felt great today," he said. "My stamina is there. I felt as strong and as loose as I was in the first inning in the sixth. I definitely could have gone back out there for the rest of the game, to be honest. It was a good sign. It's going in the right direction."
It was a much better performance than his previous start against Washington, when he was tagged for five runs and seven hits on Sunday.
"You don't take it kindly, especially when you've got to face the same team in five days," Smyly said. "You've got to make adjustments quick, or else the same thing will happen."
Smyly focused on keeping his delivery more compact on Friday and got the results he wanted. He retired the first 10 batters he faced and finished with five strikeouts and no walks.
Ian Desmond homered for Washington's only run against the lefty.
"Sometimes, I kind of fly open, trying to throw a pitch too good or too hard and leave it up in the zone," Smyly said. "I was just really working on staying in and making sure I make a good pitch down in the zone."
Though he said he tries not to think about it between starts, Smyly is eager to find out what manager Jim Leyland decides to do about the rotation.
"I guess I'm just as eager as you guys," he said. "I guess it will happen sooner or later. I don't make that call, so all I can do is keep trying to pitch well."
Rafael Soriano was scheduled to pitch, but Johnson said the reliever was still feeling the effects a root canal on Thursday. "He's recovering from a long day in the dentist's chair," Johnson said. "I sympathize with him." Soriano was expected to pitch Saturday against the Mets, but his name was scratched off the Nationals' travel roster. Johnson said the closer will instead throw in a minor league game at the team's training complex. ... The Nationals optioned RHP Cole Kimball to Triple-A Syracuse and re-assigned RHP Jeremy Accardo to their minor league camp. ... LHP J.C. Romero, who signed a minor league contract with Washington on Friday, pitched in five games for Puerto Rico in the World Baseball Classic. Romero gave up two runs in 4 2/3 innings. ... Nationals OF Roger Bernadina made a spectacular catch in the seventh inning to rob Jordan Lennerton. He received a standing ovation from much of the home crowd. ... Leyland said there was a chance OF Andy Dirks (bruised right knee) could play Saturday against the New York Yankees, but it was unlikely OF Avisail Garcia (bruised right heel) would be available. ... Leyland said he is leaning a certain way on which pitchers will comprise his bullpen, but he's not revealing anything just yet. "I have a pretty good idea how it might play out, but I can't say that for sure yet," he said. . Martinez and Fielder both had two hits and an RBI for the Tigers.