No one can say what exactly was in the cooler Drew Storen and Matt Thornton dumped on Tanner Roark after he earned his first big league save Monday night. As far as he could tell, and as far as anyone else could speculate, it was some combination of water, Gatorade and whatever other particulates accumulate in a dugout cooler over the course of a game.

Sitting at his locker after the Nationals’ 6-4 win over Miami, soaking wet with his arm wrapped, Roark didn’t seem to care much about specifics. He’d done his job, just like when he earned a Gatorade bath for his first career shutout last April.

“It was the first one” as a reliever, Roark said. “And it felt just as good as the first one.”

Coming into this season, Roark’s role with the Nationals was as unclear as the murky mixture his teammates poured on his head Monday night. Pushed from the starting rotation by the signing of Max Scherzer, unproven in late-inning short relief roles, and able to pitch at length, Roark seemed destined for no set role at all — headed for whatever-you-need, whenever-you-need-it duties. Almost every bullpen has a pitcher like that. That pitcher is rarely needed in crucial situations, and hardly ever given regular work. Roark won 15 games as a starter in 2014. He embraced the nebulous new role with his usual grin.

As April progressed and injuries and inconsistency shook the bullpen, Nationals Manager Matt Williams started pushing Roark into high-leverage innings — the ones late in games that can tilt the outcome one way or another. Roark relieved 67 times in his minor-league career, but only nine times in the majors. He had certainly not done so in high-pressure situations for a team scratching against a slippery wall of early season frustration to earn every win. Roark entered Saturday and Sunday’s games against the Mets in those situations. He pitched well in both of them, and did not allow a run.

Monday, with Drew Storen and Aaron Barrett overworked and therefore unavailable, Williams decided Roark would be his closer for the day. He did not share that information with Roark, who found out “when the phone call came in” after the Nationals tied the game at four in the eighth inning.

“I just got the call and got ready as fast as I can,” Roark said. “We eventually went up 6-4 and that gave me a big-time adrenaline boost.”

According to FanGraphs, Roark’s fastball sits around 91 or 92 miles per hour, and has throughout his career. His first pitch to Marlins pinch hitter Reid Brignac hit 94. He hit 95 later in that at-bat before striking out Brignac with a curveball. He hit 95 before allowing Dee Gordon to single on a curveball. He hit 95 twice and 94 twice as he induced a Martin Prado popout. Then Marlins slugger Giancarlo Stanton — who entered Monday’s game hitting .336 with 14 home runs in 35 games at Nationals Park — came to the plate as the tying run.

Roark fell behind 3-0. Then he pumped a 94-mph fastball by Stanton, who watched it. Roark threw 87-mph sliders on the next two pitches. Stanton swung and missed them both. Roark pumped his fist.

“He’s a great hitter. I was trying to make him chase my pitches and it worked out that way,” Roark said. “I’m just grateful for that. I’m glad we came out on top in a huge win.”

Williams said he chose Roark to fill in as closer Monday because he has “been in big moments, been in big games. It doesn’t matter to him which inning it is. It’s about getting outs.”

Williams also lauded Roark’s attitude, which has not fluctuated from his days as one of the winningest starters in the league in 2014 to his time as the versatile mop-up man in the bullpen, to his recent and crucial late-inning duties.

“He’s one of those selfless guys,” Nationals shortstop Ian Desmond said. “He just wants the ball and he wants to go out there and compete and any role you put him in, he kinda thrives it seems like. He’s definitely an asset to our team and it’s fun to watch him get better and better each time he goes out there.”

The Nationals may have found a late-inning weapon in Roark, who recorded his first strikeout of the season over the weekend and is seemingly honing his ability to reach back in key situations and find more velocity. Monday, he attributed it all to adrenaline.

“I didn’t notice” the increased velocity, Roark said. “Somebody told me when I came in here. I don’t know, I just felt good.”

He has now finished three games for the Nationals. A year after winning the sixth-most games of any starter in baseball, Roark has a save to his name.

IN THE POST

Behind an Ian Desmond home run and a 5-for-5 day from Yunel Escobar, the Nationals rallied to a 6-4 win over the Marlins Monday.

IN THE JOURNAL

Felipe Rivero’s harrowing week, which is not for those with a propensity for queasiness.

NATIONALS MINOR LEAGUES

Norfolk 3, Syracuse 1: In his first outing since his rough major-league debut last week, A.J. Cole allowed one run on seven hits in six innings. Rafael Martin took the loss, allowing two runs on two hits and two walks in 1 2/3 innings of relief. Cutter Dykstra was 2 for 5 and drove in the Chiefs’ only run.

New Britain 4, Harrisburg 2: New Britain scored four runs in the sixth to run Senators starter Austin Voth from the game after 5 1/3 innings in which he allowed two earned runs. Wilmer Difo was 3 for 4 with a double to push his Class AA average to .357, and Pedro Severino was 2 for 4.

Salem 4, Potomac 2:  Wander Suero allowed four runs in six innings and struck out three in a losing effort. Spencer Kieboom was 2 for 4 with two doubles for Potomac.

Greenville 9, Hagerstown 6: Three different Suns pitchers allowed three runs each, unaided by two errors, in the loss. Right fielder Alec Keller was 3 for 5 with two doubles and Raudy Read, Grant deBruin, Jose Marmalejos-Diaz and Osvaldo Abreu had two hits each for Hagerstown.