The hit allowed was a single to Mets captain David Wright, who went 2-for-3 in his first game of the Grapefruit League season. The third baseman said keeping his back loose is a little easier in the Florida weather.
"The back felt good today," Wright said. "We'll see how it feels tomorrow."
Giolito was staked to a 5-0 lead in the first inning. Nationals shortstop Danny Espinosa highlighted the explosion with a three-run homer.
Colon was hit hard over five innings, allowing eight runs on nine hits (three homers). But he took it in stride afterward, saying he is working to improve his stuff.
"I'm not going to change anything," Colon said. "I'll work on my breaking stuff. That's what Spring Training is for."
He gave up hits to the first four batters he faced. After a leadoff single from Michael Taylor, Daniel Murphy and Stephen Drew followed with RBI doubles. Ryan Zimmerman then singled, setting the stage for Espinosa's blast over the right-field fence.
The Nationals piled on with four more in the sixth inning for a 12-2 lead before T.J. Rivera answered with a solo homer in the bottom of the sixth.
Michael Conforto's grand slam with two outs in the ninth capped the offensive showcase.
Up next for the Nationals: Joe Ross will take the mound for his fourth Grapefruit League outing on Saturday when the Nationals face the Mets again, this time at Space Coast Stadium in Viera at 1:05 p.m. ET (watch live on MLB.TV). Ross, who is scheduled to throw five innings or 80 pitches, will be joined by most of the Nationals regulars, including Bryce Harper, Ben Revere and Anthony Rendon.
Up next for the Mets:Watch on MLB.TV at 1:05 p.m. ET on Saturday when Matt Harvey makes the start against the Nationals. "The Dark Knight" has been lights out in two starts this spring (1-0, 1.29 ERA), including his last outing, a four-inning stint vs. the Marlins where he struck out four and allowed just one hit. He was recently named the Mets' Opening Day starter.