Harper and Zimmerman hit consecutive home runs and the Nationals defeated a Miami Marlins split squad 8-7 on Saturday.
Harper connected in the fifth inning for his second homer this spring. He is batting .462 in exhibition play.
Zimmerman followed with his first home run, tagging reliever Brad Hand.
"I'm down for hitting as many as (Harper) wants to hit," Zimmerman said.
Zimmerman went 3 for 3 while serving as Washington's designated hitter.
"I haven't been worried about him," Nationals manager Davey Johnson said. "He's just a good hitter. He's got plenty of power. He's been great in BP. He's been great all the way around."
Zimmerman, who had arthroscopic surgery on his right shoulder on Oct. 25, has yet to play in the field. He has been taking ground balls and making throws to first.
Johnson is waiting until mid-March to play Zimmerman in the field. The third baseman said he no longer has to count how many throws he makes. He just throws until he is tired and then throws a little more just to give him something to build on.
"The routine plays are fine," Zimmerman said. "It's just the ones where I would have to rush and not be able to set my feet. My arm's not quite strong enough to do that yet. Once I get those going, I can build off that and get ready to go to the games."
Zach Walters hit his second spring homer in the eighth for the Nationals.
Washington's Chris Young struggled in his first spring start, allowing three runs in three innings while also walking three.
Johnson said he thought Young looked "rusty." Young had another word for it, calling his outing "erratic" as he struggled with fastball command and his release point.
"It's pretty consistent for where I am every spring in my career," Young said. "It just takes a little time to lock in mechanically and by the end of spring it comes around."
Miami starter Alex Sanabia lasted 2 2/3 innings, giving up four runs and five hits. After retiring the side in order in the first inning, he struggled in the next two.
Sanabia, a candidate for the Marlins' rotation, was making his second start of the spring.
"It came down to mechanics, just being out in front a little bit and not staying back a little bit longer," Sanabia said. "A minor thing will make a big difference, you know?"
Nationals RF Jayson Werth felt tightness in his right forearm following Friday's game and was originally going to be a scratch from Saturday's lineup. But he told Johnson he was ready to go and ended up going 1 for 3. Werth felt the tightness after retrieving a ball hit off the wall and throwing sidearm. ... Nationals RHP Nathan Karns, who has been experiencing tightness in his right leg, was examined by a doctor. Johnson said Karns passed all of his tests and will throw on the side Sunday to see how he feels. ... The Nationals host the Braves on Monday and Johnson told reporters Braves manager Fredi Gonzalez wanted to skip the designated hitter rule and have the pitchers bat. Johnson, however, said he would not agree to it because he still wants to use Zimmerman as a DH. ... The Marlins did not commit any errors. They've made eight in 12 games.