His master launched two long home runs, including a tiebreaking drive in the eighth inning, and also doubled to lead the Nationals over the Mets, 7-6.
"He crushed a couple of balls. What a day he had," Nationals manager Davey Johnson said.
Although Swag missed the show, the brown Labrador retriever soon will be joining his master.
"He's coming to live with me in about two weeks," Harper said. "He's a great dog. I can't wait to have him."
Good dog, great player.
Nationals players aren't required to be at the ballpark until 11 a.m. for a day game after a night game. Last Saturday in Washington, in a similar situation, Harper was an early arrival, devouring breakfast the way he does his light workout.
Two-and-a-half hours before game time, with the gates at Nationals Park not yet open, Harper left the cap of his hometown UNLV Rebels on his locker shelf. He grabbed his Nationals cap, flipped it on visor-to-the-rear to conceal his Mohawk-gone-wild hairdo and headed to the field, just beyond the first-base dugout, to do a pregame interview for the Fox national broadcast.
The stadium still was virtually empty. Harper just seems to do everything ahead of the masses.
Harper, now 20, was on the cover of Sports Illustrated at age 16, was the youngest player in the majors at 19 on his way to winning NL Rookie of the Year honors last season, and kicked off this season by becoming the youngest player to homer twice on Opening Day.
Braves manager Fredi Gonzalez said he enjoys watching the youthful exuberance from the opposing dugout.
"As long as he stays healthy, this guy is going to be some kind of player to watch, and baseball needs those type of players -- the young phenom who comes in and excites everybody,'' Gonzalez said. "He plays the game the right way. When he hits a ground ball to short, he busts his butt down to first base. If he hits a single, you know he's looking to take the extra base.
"If you don't make good pitches against him, he's going to hurt you. Not just that. He can beat you on the basepaths, beat you defensively, hit one out of any ballpark or bunt for a hit.''
Nationals centerfielder Denard Span says Harper has the "it" factor.
"You can't teach instincts, especially when the [bright] lights are on,'' said Span, impressed by Harper's maturity at such a tender age. "When it's game time, he brings his A-game and that excitement to the team and to the fans.''
As much as he might like to carry his team, Harper understands that's not how it works. So far, in his young career, he's made it a point not to hoard media attention and goes out of his way to spread the credit for Washington's success.
"This is a team sport. It's not a one-guy thing,'' he said. "[Winning] the World Series is the biggest thing in my mind, and if I can play well, I can help my team get there.''
Nationals outfielder Jayson Werth petted a couple of Labrador retrievers and teammate Danny Espinosa greeted a dachshund as 500 dogs paraded on the warning track before the game. Werth and Espinosa later doubled.
Although the Mets didn't homer for the first time in eight home games this year, they do have a history that links homers and dogs: Before Mr. Met, their first mascot was a beagle named Homer.
In 1962, Homer was supposed to run around the bases at the Polo Grounds after the Mets connected. The first time he tried to do it in a game, the story goes, he reached second base and took off on a sprint for centerfield.
With Seth Livingstone