Virginia’s Mike Papi, center, is mobbed by his teammates after his two-out double in ninth lifts the Cavaliers to a win against Mississippi in their College World Series opener on Sunday night. (Brynn Anderson/Associated Press)

It already had been a memorable Sunday for Joe Papi — a Father’s Day spent watching his son play in front of a packed stadium at the College World Series. He wasn’t sure it could get any better.

But with one ninth-inning swing of the bat, it did.

From his seat near the concourse behind the third base dugout at TD Ameritrade Park, Joe Papi had a bird’s-eye view of the natural, left-handed stroke he first witnessed in his driveway when Virginia first baseman Mike Papi was 3. His son’s walk-off double gave the Cavaliers a dramatic, 2-1 win over Mississippi and spawned an on-field moshpit afterward.

A day later, Joe Papi still struggled to put the moment in perspective, even if Mike Papi is beginning to make such heroics commonplace.

“Normally I’m stoic like he is, but it doesn’t seem real what’s going on right now,” Joe Papi said. “His swing is the gift he has.”

Virginia’s soft-spoken junior slugger is a luxury few teams enjoy in this College World Series, in which runs have been scarce and home runs even scarcer. And he likely will figure in prominently again when the Cavaliers take on TCU on Tuesday night with a chance to move within one win of the championship series in what is expected to be another pitcher’s duel.

The Horned Frogs will start left-hander Brandon Finnegan, selected by the Kansas City Royals with the No. 17 pick in the Major League Baseball draft earlier this month, against Virginia southpaw Brandon Waddell.

During a season in which Virginia’s lineup has underwhelmed, Papi has been one of the team’s few constants. He hits for average (.314), leads the Cavaliers in home runs (11) and RBI (55) and ranks second in the country in walks (56). In seven NCAA tournament games, he is a scorching 14 for 29 at the plate with eight RBI, which is of particular importance considering Virginia has left a staggering 68 men on base during that time.

But it was the at-bat Sunday night that proved to be quintessential Papi: powerful, patient and perfectly timed. He worked Mississippi reliever Aaron Greenwood to a full count, waiting until Greenwood threw a 79-mph change-up over the heart of the plate. Joe Papi was shocked to learn his son didn’t know what pitch had come his way because “he always knows what he’s swinging at.”

Mike Papi says his selective approach is “something that’s evolved in my game as I’ve matured,” even though it sometimes drives his father nuts.

“I was always after him, and I still am: ‘You’ve got to expand the strike zone.’ He won’t do it,” said Joe Papi, a former school principal in Northeast Pennsylvania who served as an assistant coach for his son’s high school team. “He’ll take a third strike call, and he’ll say, ‘Dad, that was a ball.’ But that’s what helped him catch the eye of the pro [scouts].”

Papi, a first-round pick by the Cleveland Indians this year, was not a regular in Virginia’s lineup just 15 months ago. Slowed by a back injury, he did not emerge until a March 2013 game against Clemson, promptly hitting a game-tying, pinch-hit single in the ninth inning and crushing a go-ahead home run in the 11th.

He then finished last year second in the country in on-base percentage (.517) and led the ACC in batting average (.381). These days, Coach Brian O’Connor calls him one of the best hitters to come through Charlottesville.

“He didn’t get caught up with whether he was playing or not, and that was obvious when he did get his turn,” Virginia hitting coach Kevin MacMullen said. “He was prepared for that opportunity. He wanted to prove something to his teammates.”

Those same teammates mobbed him on the field Sunday night, but the whole scene caught Joe Papi off guard.

“When you see him jumping around and happy like that — which was totally appropriate in that situation — it is still uncharacteristic,” he said. “He’s a very controlled, stoic kid, which helps him in the box but maybe makes him look aloof during a celebration.

“But in the College World Series, you’ve got to let it fly.”