The Nationals prospect tied a career high with 10 strikeouts and allowed four hits over 6 2/3 innings Friday as Class A Advanced Potomac blanked Myrtle Beach, 3-0.
Karns (1-2) retired his first seven batters and did not allow a Pelican to reach second base until the fifth inning, when Jake Skole walked and Edwin Garcia singled with two outs. He ended the threat by getting Brett Nicholas to line out to left field.
The 24-year-old right-hander exited in the seventh after allowing a two-out single to Tomas Telis and walking Skole again.
"Today, I was working off my fastball," said Karns, who was selected in the 12th round of the 2009 Draft. "I was working ahead of the hitters and controlling the at-bats for the most part. The defense made quality plays; it seemed like when I was trouble, they made plays behind me. It's pretty easy to pitch when they do that."
It was Karns' first Carolina League win in three tries since being promoted from Class A Hagerstown on June 5. He had been 0-2 with an 8.53 ERA for the P-Nats.
"I think I'm just settling in," Karns said. "I'm catching the speed of the game, starting to feel comfortable, and every day I continue to work on things that I've been struggling with. Lately, that's been my fastball command and getting ahead of hitters. Today, things started clicking and the results speak for themselves."
Karns also fanned 10 in his final start for the Suns on May 26, tossing a seven-inning one-hitter at Lakewood.
The Texas Tech product believes the formula for success at this level is simple.
"Continue to throw strikes, work ahead of hitters and try to keep the count in my favor, rather than the hitters' favor," he said.
Jimmy Barthmaier took over in the seventh and, after committing a balk, struck out Garcia to end the inning. Rob Wort allowed a hit and fanned four over the final two innings to earn his fifth save.
Zach Walters gave the Nats a lead with an RBI double in the seventh and Michael Taylor added a sacrifice fly.
Myrtle Beach starter Kyle Hendricks did not figure in the decision after yielding three hits over six shutout innings.