The Mets surrendered four homers in all, as Baltimore teed off on Jeremy Hefner in the fifth and sixth innings following a four-frame outing from starter Dillon Gee.
McLouth commenced the third with a towering drive just to the right of the 400-foot indicator in straightaway center field. Manny Machado followed with a double, and the 20-year-old scored on a Matt Wieters single later in the inning.
McLouth got back to work in the fifth, when he sliced Hefner's second pitch over the fence in left. A healthy wind blowing out toward left field guided the ball into the stands. Chris Davis followed with a two-run shot of his own later in the inning, and Steve Pearce added his team-leading seventh homer of the spring in the sixth.
Eight of Baltimore's nine starters recorded at least one hit.
"I'm happy we ended this way," said Miguel Gonzalez, the Orioles' starting pitcher on Saturday. "Nate McLouth had a great day today."
Gee allowed three runs on six hits in four innings, while tallying four strikeouts. He wrapped up the exhibition slate with a 5.87 ERA and 18 punchouts in 23 innings. Hefner yielded four runs -- on three homers -- with two strikeouts in two frames.
Gonzalez stymied the Mets for five innings, limiting New York to just one hit -- a Marlon Byrd single -- while logging four strikeouts. The Mets scratched across their only run when Ruben Tejada plated Byrd with a sacrifice fly in the fifth.
"I'm feeling pretty good about myself," Gonzalez said, "and the fact that we ended this way gets me pumped up a little more in looking forward to the season."
Up next: The Mets have Sunday off before hosting the Padres at Citi Field for their season opener at 1:10 p.m. ET on Monday. In that affair, Jon Niese will take the hill for New York. He'll be opposed by Padres right-hander Edinson Volquez.