Nate Karns gets a hug from his mother, Tambra, after his major league debut on May 28 against the Orioles at Nationals Park. (Jonathan Newton/THE WASHINGTON POST)

After he concluded an on-field postgame interview following his surprising major league debut last week, Washington Nationals pitcher Nate Karns spotted a familiar face.

His mother, Tambra, had made her way down from the stands at Nationals Park with her husband, David, and Karns’s girlfriend and stood near the railing next to the dugout.

Karns, who hadn’t seen his mother since before big league spring training, stopped to give her a hug. Tambra had controlled her crying through most of Karns’s performance against the Baltimore Orioles. But upon seeing her son, who had overcome major shoulder surgery and stood by her side as she struggled through cancer and a debilitating stroke, the tears couldn’t be stopped. He whispered “thank you” in her ear, but she stopped him to say the same back.

“My mom has been through a lot and she has done a lot for me,” said Karns, who is scheduled to make his third start of the season against the Minnesota Twins on Sunday. “It was really nice that I was able to show that all her sacrifices paid off for me and I didn’t waste whatever she gave me and took full advantage of it.”

The Nationals reached down to Class AA Harrisburg early last week in desperate need of a starter following an injury to Ross Detwiler. Karns, 25, was among their top three choices to fill in when needed, even though he had only pitched nine games above Class A.

The Post Sports Live crew looks at the issues plaguing the Washington Nationals, including injuries to Bryce Harper and Stephen Strasburg and the team’s poor defense. (Post Sports Live)

He had overcome a death knell of an injury — a torn labrum in his throwing shoulder — in 2010, followed by an arduously long rehab in Viera, Fla., to reach this point.

So when he displayed impressive poise as he held the potent Orioles lineup to three runs over 41 / 3 innings and earned two more starts, Tambra wasn’t surprised. He endured her battles with two forms of cancer when he was younger.

He made the decision to transfer colleges following his freshman season to be closer to her after her epilepsy led to a stroke in 2007 and temporarily gave her amnesia.

“At an early age, he took on a lot of responsibility,” Tambra said.

Tambra kept much of the details of her illnesses from Karns — and his younger sister, Amanda — because she knew he had enough to deal with. He was pursing his college degree and baseball career, a well-regarded right-hander out of James W. Martin High in Arlington, Tex. But after he returned from North Carolina State following his freshman season, his mother suffered the stroke that made her forget her name and the names of her family members.

Karns decided he wanted to be closer to her. He transferred to Texas Tech. He made the 41 / 2-hour drive home often. He talked with his mother several times daily. “I had that security of knowing that I could drop everything and get in my car and get home,” he said. Tambra didn’t want him to move.

“That’s a big weight to bear,” she said. “I have tremendous respect for him. It took a lot.”

Karns applied the same resolve and calm when, after pitching in college with what was originally diagnosed as bicep tendinitis, he learned he had a torn labrum in his throwing shoulder. He first felt the discomfort his junior season but still pitched well. After the Nationals drafted him in the 12th round in 2009, Karns sputtered in spring training and extended spring training.

He underwent shoulder surgery and made his minor league debut in 2011 at 23. He fulfilled his potential last season, punching up a 2.26 ERA at Class A Potomac and earning the organization’s minor league pitcher of the year award. Some pitchers struggle to recover from shoulder injuries and others don’t ever return the same.

Karns, however, was on a major league mound last week firing mid-90’s fastballs, a story of a player’s resolve and the success of all facets of an organization from scouting to player development to rehab.

“The first couple years rehabbing built a foundation for me mentally,” he said. “I had to translate that into going out and performing on the field and I think I did a good enough job. I really wanted to return the favor for all I had to put the organization through with surgery and rehab and a late career.”

Now, Karns can focus solely on baseball. His mother’s cancer is in remission and overall, she said, her health is better.

She is back at work as an interior designer. She and her husband, a military reservist, were again in the stands on Sunday in Atlanta cheering on Karns in his second start.

He gave up four runs, only three earned, over 42 / 3 innings and struck out six batters.

“I’m so happy and so proud,” Tambra said. “He deserves this for more than just his hard work and effort, but just from a mother’s standpoint for everything he did for me. I wish I could give him more. Just to see him reach his dream is such a reward for me.”