Washington Nationals outfielder Bryce Harper, right, talks with relief pitcher Ian Krol.

It all happened so fast for Ian Krol.

Before he knew it, he was called up to the Washington Nationals’ 25-man roster from Double-A Harrisburg on Tuesday. And little did he know that he’d make his major league debut Wednesday against the New York Mets.

Running out of the bullpen during the middle of the sixth inning, Krol felt butterflies stirring inside his stomach. The 22-year-old native of Naperville, Ill., didn’t know what to expect.

“I wasn’t thinking about the situation, the big stage, all that,” said Krol, who entered with the Nationals down 7-1 in a game they’d lose 10-1. “I was trying to focus and do my job.”

Krol’s family had recently watched him pitch in Harrisburg and decided to make the trip out to Washington just in case he was called upon this week.

After giving up a leadoff double, Krol struck out the side, which included Mets third baseman David Wright and second baseman Daniel Murphy. His fastball routinely hit the mid-90s, reaching as high as 96 mph.

With the Nationals designating Henry Rodriguez and Zach Duke for assignment, Krol has an opportunity to work his way into becoming one of Washington’s regular relievers.

“If he continues to throw good throws then there will be some good signs,” manager Davey Johnson said.

Krol was originally drafted out of high school by the Oakland Athletics in the seventh round of the 2009 MLB draft. After spending four seasons in Oakland’s minor league system, he became the player to be named later in a three-way trade that sent Michael Morse to Seattle and netted the Nationals pitching prospects A.J. Cole and Blake Treinen.

Krol said he was given no indication when he’d make his debut. For him, being called up was an accomplishment in its own right.

“It still hasn’t sunk in yet,” Krol said. “To be honest with you, I’m on cloud nine.”