BOSTON — Back in late August of 2011, an overly-hyped 19-year-old named Bryce Harper created a buzz at Hadlock Field, appearing with the Harrisburg Senators (though he was injured and did not play).

In that same month, the Red Sox signed their own 19-year-old, an infielder drafted in the fifth round. Few took notice when Boston offered $700,000 to Mookie Betts, convincing him give up his baseball scholarship to the University of Tennessee.

Betts eventually reached Hadlock Field in 2014 and, a year later, he crossed paths with Harper at Fenway Park.

Actually, Betts got in the way of a ball hit by Harper – more specifically a long fly ball in the first inning that was going to land in the Red Sox bullpen for a two-run homer.

But the ball never made it. Betts, now a center fielder, leaped in front of the wall in right-center field and his glove swallowed Harper’s blast.

“He’s got ups,” Harper said. “It’s pretty impressive to see him jump over the wall like that and rob a home run … Great players make great plays.”

Betts was hardly done, making the most of his first home opener at Fenway.

He walked in the first inning and stole two bases on the same play, before scoring.

In the second inning, Betts turned on an inside fastball from Jordan Zimmermann and sent it quickly over the Monster for a three-run homer.

In the third inning, he grounded a single for another RBI.

“The first two or three innings, Mookie took the game over, defensively, base-running, at the plate,” Boston Manager John Farrell said. “Exciting player.”

In the fifth inning, Betts sizzled a line drive out to center fielder Michael Taylor. In the seventh inning, Betts showed mortality and struck out.

He finished 2 for 4 with a walk, home run, four RBI and two stolen bases – and, oh, that catch.

“That was a game-changer,” Boston starting pitcher Rick Porcello said. “That could have meant two runs and put us in an early hole.”

“The way (Betts) played today, it was a lot of fun to watch. He pretty much did everything.”

Betts, who is only 5-foot-9 but can dunk a basketball, said the ball was high, giving him time to reach the wall.

Betts is wowing them in Boston like he thrilled those at Hadlock in April and May last year.

He is the spark that Boston has needed since it lost Jacoby Ellsbury to free agency and the Yankees after the 2013 season.

Remember Ellsbury’s electrifying steal of home at Fenway in 2009? Another Hadlock-to-Fenway dynamo, Ellsbury was must-see viewing when he raced around the bases.

So is Betts.

Betts gave a hint of his speed and daring last July with his infield double at Fenway. He beat out a ground ball and, when he noticed no one was covering second base, took off and made it.

In the first inning Monday, with Betts on first and the Nationals in their shift against David Ortiz, Betts stole second.

He slid in safely , immediately popped up and looked at third base. Sure enough, no one was covering third and Betts took off. Zimmermann ran over to cover, but his tag was too late.

“Once I knew I was safe (at second), I looked up to see where the pitcher was and he was hanging around the mound,” Betts said. “So I figured I would go.”

The Nationals challenged the play, but Betts was safe. He scored on Ortiz’s single.

At the plate, Betts has been struggling with breaking balls (he’s batting .233).

But give him a fastball …

In the second inning, Zimmermann came inside with heat. Betts pounced.

“The home run he hit was a fastball in, off the plate,” Porcello said. “You don’t see too many guys turn on a ball like that.”

After the game, Betts was mobbed by reporters, asking him about every play, about his career, and even what he had for breakfast (omelet, two pancakes).

But Betts quickly put matters in perspective. Yes, he has two home runs this year. He has also struck out eight times.

“I’m confident but I keep on swinging at sliders in the dirt,” Betts said. “There are positives, but I look at what I have to work on.”