Strasburg, slated to take the mound on Opening Day at Citi Field, gave up three runs on five hits in 5 2/3 innings, walking two and striking out seven. Wheeler, lined up to pitch the third game of the season, was knocked out after 2 2/3 innings, having allowed five runs on five hits, with three walks and one strikeout.
"I think it affected the way I attacked them," Strasburg said of his Opening Day opponent. "But you get out there in the heat of the moment and you definitely want to go out there and compete, so I wasn't just giving in to anybody."
Harper provided the big blow off Wheeler, who ran into some bad luck in the third inning. With one out, Denard Span and Anthony Rendon hit consecutive infield singles, and Jayson Werth walked to load the bases before Ryan Zimmerman squeezed a two-run single through the left side of the infield. Harper then jumped on a Wheeler fastball and crushed it over the wall in deep left-center, where it caromed off the top part of a flagpole for a three-run shot, his second homer this spring.
"My [left] knee feels great," said Harper, who had surgery on the knee this offseason. "That's what I kept saying: That's all I cared about. My swing's going to be there, I know that. My offense stuff is going to be there. My arm's going to be there. I'm just excited that I have no pain. That's the biggest thing that I tried to get over this spring. I'm excited to go into the season."
The Mets had struck first against Strasburg in the top of the frame. d'Arnaud led off by belting a hanging breaking ball over the left-field wall for his second homer of the spring, both in the past three games. One out later, Strasburg walked No. 9 hitter Ruben Tejada, and Eric Young Jr. ripped an RBI triple into the right-field corner, with Tejada narrowly beating the throw home. David Wright capped the scoring with an RBI single.
Jose Lobaton added an RBI single off Scott Rice in the fifth inning for Washington, Span finished with three hits and a walk out of the leadoff spot, and Zimmerman added a solo homer in the seventh to finish the day with three RBIs.
Up next: The Nationals will play their next-to-last Grapefruit League game on Wednesday, when they travel to Jupiter, Fla., to face the Cardinals at 1:05 p.m. ET on MLB.TV. Left-hander Gio Gonzalez is set to make his final spring start, opposite St. Louis ace Adam Wainwright. Gonzalez, slated for the No. 2 spot in the rotation, has a 2.70 ERA in four outings. Craig Stammen, Aaron Barrett, Ross Detwiler and Xavier Cedeno will be available in relief.