WASHINGTON -- Stephen Strasburg was pulled from Sunday's game after five innings and 90 pitches at Nationals Park because of tightness in his golden right arm.

After the Nationals' 9-3 victory over the Orioles, Nats manager Davey Johnson called the problem tightness in Strasburg's right biceps. Strasburg emphatically said it was general arm fatigue.

No matter. Johnson was concerned enough about the issue that he yanked Strasburg with a 6-3 lead after he struck out eight, all of them in the last 12 batters he faced.

"I don't care who it was, when I find out they have a little tightness in there and they're worried about it, they're out," Johnson told the media after the Nationals salvaged the final game of a raucous three-game Battle of the Beltways series. "I'm not that concerned when I hear it's in the biceps. That's where you get some tightness sometimes, throwing a lot of pitches in an inning. It's kind [of] borderline being a little tired."

The Nationals have to be concerned about Strasburg, given his injury history and the strict 160-inning limit that has been placed on him for this year. When he reaches that figure, he's apparently done, Johnson has said, adding that he doesn't believe the latest problem will lead to Strasburg missing his next start on Saturday in Atlanta.

Strasburg was the top pick in the 2009 First-Year Player Draft, and the Nationals invested four years, $15.1 million and much of their future in him.

"It wasn't my biceps," Strasburg responded when asked about the problem after a game in which he hit his first Major League home run, a back-to-back shot with two outs in the fourth inning behind catcher Jesus Flores. "It had nothing to do with my elbow or anything. It was just normal fatigue. It got a little tired, got a little tight. But that's nothing different than any other outing. It's probably going to be like this for the rest of the year. It's part of coming back from Tommy John, building up the innings. It's something I've just got to be smart about."

Strasburg, a San Diego native, said he broke his regular routine and worked extra hard after losing his last start, 6-1, here to his hometown Padres on Tuesday. In that one, he lasted only four innings, allowing four runs on seven hits while striking out five.

That effort contributed to sluggishness as he warmed up before Sunday's game in the bullpen. When he took the mound and threw three consecutive balls to Orioles left-fielder Xavier Avery, opening the game, Strasburg said he knew "something wasn't right."

Strasburg ultimately worked Avery to a full count before allowing a single. J.J. Hardy hit a mammoth shot to the warning track in center, moving Avery to second and he scored on a Nick Markakis single. Only Adam Jones bouncing into a double play kept Strasburg's pitch count at 15 in the first inning. But when Bryce Harper dropped a ball in left-center for a two-base error to open the second, that led the way to seven Orioles coming to the plate in the inning and a pair of unearned runs.

The Orioles led, 3-0, at that point, and the damage seemed to be done. Strasburg ended the inning by striking out Hardy. The Orioles didn't have another baserunner against him, as Strasburg set down the last 10 batters he faced and the Nationals came back to score nine times.

Johnson said he became aware that Strasburg was having arm problems when he found him in the tunnel behind the dugout after the top of the fifth inning, working on an arm flexor machine. At that point, Strasburg hadn't advised the veteran manager that he was experiencing tightness. At that juncture, he finally did.

"Stras is not a complainer," Johnson said. "If he had told me that it was tight after the first inning, I would've hooked him then to be on the safe side."

Johnson was not the manager two years ago when Strasburg splashed on the scene as a phenom and went down with his elbow injury -- Jim Riggleman was. Johnson was named manager last year at midseason when Riggleman resigned because of a contract dispute. The fact is that the Nationals shut down Strasburg in 2010 when he complained about shoulder tightness during a pregame bullpen warm up. Strasburg didn't start that game, and was placed on the disabled list. But he injured his elbow when he returned.

So there is obvious precedent for concern when the 6-foot-4-inch Strasburg is suffering even minor arm problems. Strasburg was handled with kid gloves by head coach Tony Gwynn in his junior year at San Diego State. Gwynn limited him to one start a week in what came to be known as Strasburg Fridays. As a Major Leaguer, he has made only 26 starts in a five-man rotation, nine of them this year.

Strasburg said he was upset enough about his last start, coming after a win at Pittsburgh on May 10 when he whiffed 13 in six innings, that he "overworked" in the days leading up to Sunday. He's now 4-1 with a 2.21 ERA and a Major League-leading 64 strikeouts.

"I was being a little immature in between, and I was throwing a lot more because I didn't like the way I pitched the last time," he said. "That's the thing I need to change. I just can't change my routine because of an outcome."

Strasburg said he was frustrated about coming out of Sunday's game and not throwing at least six innings. Sitting on the dugout bench, Strasburg told Johnson that his arm felt more relaxed as time transpired.

Strasburg told Johnson the same thing he later told the media: Not to worry.

"My biceps is fine," he said.