It came at Yankee Stadium in the 11th inning of a tied All-Star Game. McLouth had entered the game in the bottom of the fifth, taking over for Chicago's Kosuke Fukudome in center.
Heading into the 11th, the Pirates center fielder had made two routine catches. But with the potential winning run on second and one out, Texas' Michael Young laced a single into center that appeared to seal a sixth straight AL All-Star win.
McLouth charged in and threw toward home, with Rays catcher Dioner Navarro lumbering toward the plate. McLouth's throw was perfectly executed, as was the grab by catcher Russell Martin on the other end.
"That was right on the money," Martin said, afterward.
Navarro was tagged out. The game continued.
"The game's going to be over if that doesn't happen," said McLouth, who has three assists with Pittsburgh this season. "In that situation, you've got to know that they're going to be sending him. I came up throwing all the way."
And with that, McLouth unofficially made himself known.
Though that was the apex of the night, McLouth's impact on Tuesday's game would be far from over. He beat out a bunt in the top of the 12th that also advanced St. Louis' Ryan Ludwick to second with no outs. McLouth, however, would end the inning stranded at second.
In his fourth at-bat of the night, McLouth nearly gave the NL an extra-innings lead with a deep drive to right that was caught on the warning track to lead off the 14th frame.
"I knew it was going to be close," said McLouth, who has a team-leading 19 home runs this season. "I hit it well, but I got under it. I knew it would be close, but I didn't think that it would go out.
"It was a great time anyways."
Back in the seventh, McLouth's first All-Star plate appearance ended with a lazy flyout to center. He then lost the battle against Yankees future Hall of Famer Mariano Rivera in the 10th when he struck out looking on a 3-2 pitch.
Because the game went 15 innings, tying it for the longest contest in All-Star Game history, it was as if McLouth had started on Tuesday night. He played 11 innings in the field, while Fukudome, who was the elected starter, played just four.
The fact that McLouth played on Tuesday as if he belonged, didn't come as a surprise to those who had followed his two-day All-Star experience.
Maybe he is just a quick learner, but it appeared to those congregated at Yankee Stadium on Tuesday that the Pittsburgh center fielder is simply preparing himself for making this All-Star experience somewhat of a frequent occurrence.
Game-time nerves? Nope.
"I was just more excited more than anything," McLouth said.
He definitely made a rookie mistake by waiting around on Monday to watch the Home Run Derby in its entirety, only to face a traffic logjam try to get home, right?
"The one thing I hate is traffic," said McLouth, who wore a microphone for MLB.com during the Derby. "I was going to beat that at all cost. I stayed for the first round and then tried to beat the traffic."
Oh well, so much for the first-time learning curve.
But maybe McLouth has reason to be comfortable. And maybe seeming as familiar with the protocol as a number of the veteran All-Stars is just yet another sign that McLouth believes that he should be playing alongside the best in the game.
While being a part of such a memorable Midsummer Classic at storied Yankee Stadium topped McLouth's All-Star experience list, it was far from the only memory he'll be taking from New York City.
From participating in a Red Carpet Parade that he termed "phenomenal" to taking batting practice in front of close to 40,000 people, McLouth soaked in the total experience. He had been urged by teammates Freddy Sanchez and Jason Bay, both recent Pirates All-Stars, to enjoy every minute and to take it all in, despite how daunting a task that could seem.
"It was a great experience and the way it played out -- except for not winning the game -- I wouldn't have changed anything," he said. "I think I played OK. The main thing is that it was a great time."
Jenifer Langosch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.