As the Washington Nationals celebrated their National League East title Monday night, standing on their own field soaked in champagne and talking for nearly an hour about every baseball subject imaginable, one subject came up that had a perplexing, surprising but exciting answer.

Since Manager Davey Johnson called a team meeting in Miami on Aug. 29 with the club mired in a five-game losing streak, which player had done the most to help the team right itself and go on a solid 19-13 run to end up with the division title? Gio Gonzalez was 5-1 with a 1.34 ERA. Ryan Zimmerman had 27 RBI. Ian Desmond hit .333 and fielded brilliantly. Drew Storen was lights-out: 1.17 ERA in 17 games. Adam LaRoche hit nine homers.

But the Nats were not surprised to learn that the best offensive player in the game from Aug. 29 until now was on their team, leading MLB in that span in runs, extra-base hits and on-base-plus-slugging percentage (1.106) with 10 homers. The teenager.

The legend of Bryce Harper has become big league reality in the past five weeks, though few have realized just how dramatically.

“That kid was in every big play we had down the stretch,” reliever Craig Stammen said. “He stepped up when it counted. When the lights are on, that boy shows up. That’s just the way it is.”

And that may be the way it is for a long time. In the first mega-test of whether the Nats’ center fielder, still only 19, can be a huge star, Harper has totally burned down the house.

We’re no longer talking about the hype of Harper that’s swirled since he was 15.

This is the real time-to-put-up deal. In this span when Harper was slugging .699 and hitting .341, the Angels’ 20-year-old star, Mike Trout, hit .269 with just nine RBI as his team eventually was eliminated.

Harper is so much more than numbers. You can feel him in the game like part of the atmosphere. He has run wild on the bases, tagging to go from second to third on an infield popup or pulling a delayed steal of third that draws a wild throw to score him. He has stolen hits with wall-crashing catches in center and received two standing ovations in one inning for his cannon throws to the plate. Most of all, he seems focused, in control and like he’s having a ball. The temper that derailed him during a two-month slump? Gone for now.

When he was still in high school, Harper said he wanted to be the greatest player who ever lived. Didn’t predict he would be. Said that was his only goal. Nothing less. Since Aug. 29, Harper hasn’t been Mickey Mantle. (Harper wears No. 34 because the numbers add up to 7, the Mick’s number.) He has been more like Willie Mays, playing every facet of the game with flash, dash, power, abandon and a ferocious desire to dominate his foes.

“It’s not a surprise. He’s a big-game player,” Jayson Werth said. “I give him hell all the time. He’s always saying, ‘This is how I do it,’ and, ‘This is my way of making that play.’ I say, ‘You haven’t done jack. There is no “your way.” ’ But, yeah, I believe in him.”

Is Bam-Bam really that good? We don’t know. Earlier this year, he had a two-month slump. He still misjudges about one long flyball every 10 days. Two years ago, he was a catcher; now, like Mantle in his early years, he plays center like a wild bull — sometimes wrong, but always in a hurry.