Stephen Strasburg stared ahead from the dugout, face drained of expression, a pinch of chewing tobacco tucked in his lower lip. His pitching coach, trainer and manager huddled around and took turns speaking to him. They told Strasburg, in a one-sided conversation, that the game — his game — would continue without him.

Strasburg exited after two innings Friday night from the Washington Nationals’ series-opening, 3-2 victory over the Atlanta Braves. He left with a strained right oblique, an ailment that had bothered him for much of May. The right-hander took a flight back to Washington after the game for further tests. He tried to convince Nationals personnel to let him keep pitching and hopes to make his next start, but pitchers can miss up to six weeks with this type of injury.

“It’s something where, the last few starts I’d feel it warming up,” Strasburg said. “I’d go out there and I wouldn’t feel anything. Tonight, it was more kind of like the reverse. I felt really good in the bullpen. I threw a couple pitches in there, and it started to tighten up. I felt it more and more. Nothing I could do about it. I’m kind of frustrated.”

As Strasburg digested the news that he would not pitch, even if his prized, surgically repaired right arm had been spared, another dose of optimism had drained from the Nationals’ season.

Out beyond the right field fence at Turner Field, in the Nationals’ bullpen, Craig Stammen sprung out of his seat. The right-handed long reliever prepares each day for emergency, and here was the biggest — the Nationals entered a .500 team, and their resurgent ace sat in the clubhouse with 21 outs to record against the National League East rival they trailed by 51/ 2 games.

The Post Sports Live crew discusses what would happen to the Nationals’ lineup if Bryce Harper keeps suffering minor injuries. (Post Sports Live)

Word of Strasburg’s ailment had spread to Stammen and bullpen catcher Nilson Robledo. In the first inning, Robledo told Stammen, “Be ready. His shoulder’s hurting.”

“He’s throwing 98,” Stammen replied. “His shoulder’s not hurting.”

Then Stammen started seeing Strasburg grimace.

“The second inning, you could just tell he was laboring a little bit,” Stammen said. “He just didn’t look the same. So, I guess I kind of got ready. I was praying he could keep going.”

Stammen’s performance could not overshadow the black cloud Strasburg’s injury presented, but he lifted the Nationals to a potentially galvanizing victory with four dauntless relief innings, retiring all 12 hitters he faced while recording three strikeouts. The Braves had prepared for Strasburg’s high-90s heat and disappearing change-up, and Stammen baffled them with his darting sinker and a devastating slider.

“I’m pretty sure once Stephen came out, those guys were like, ‘Ooh, we got to the long relief guy,’ ” center fielder Denard Span said. “Stammen came in and did a hell of a job.”

In the seventh inning, Tyler Clippard rode down a mountain in an 18-wheeler with the brakes cut and escaped with mere scratches. He allowed a run and loaded the bases with one out by hitting consecutive batters with pitches. He then struck out Dan Uggla, and with his 32nd pitch of the inning, he got Chris Johnson to chase an 83-mph change-up in the dirt.

The Post Sports Live crew debates which injured player’s return would be the biggest help to the Washington Nationals’ struggling offense. (Post Sports Live)

Drew Storen and Rafael Soriano finished what Strasburg had started. The Nationals’ lineup again floundered without Bryce Harper, but leadoff hitter Span swatted two triples among his three hits and scored two runs, just enough for the Nationals to cut their deficit in the NL East to 41 / 2 games. Their biggest win of the season coincided with the scariest moment.

“It was a great win,” Manager Davey Johnson said. “But Stras is a big loss. He wanted to continue. He was wincing and in a whole lot of pain. I was not so much worried about his back as I was worried about his arm. Anytime you have something like that, you worry about putting more stress on your arm.”

Johnson said the Nationals had not planned to place Strasburg on the disabled list until a further diagnosis. However, after midnight Class AAA Syracuse pitcher Erik Davis, a right-hander on the 40-man roster, revealed on his Twitter account he had been promoted to the majors. It’s possible Davis will be coming up for Bryce Harper, whom Johnson said earlier could land on the DL with left knee bursitis.

The victory lessened the sting of losing Strasburg, whose status will hover over the Nationals until he next takes the mound. Strasburg appeared uncomfortable as he pitched through his second inning, which began with a deep home run by Freddie Freeman. Strasburg struck out the next hitter, Evan Gattis, as he twice hit 98 mph with his fastball.

In the next at-bat, against Brian McCann, Strasburg threw two consecutive change-ups, the pitch most difficult on his arm — it was the pitch he threw in 2010 when his ulnar collateral ligament snapped. On his next pitch to McCann, his fastball dipped to 94.

“It was more so after I threw the pitch,” Strasburg said. “I think that was kind of affecting the way I was finishing everything. It’s kind of hard when you know what you’re going to feel after you throw the pitch. You just kind of go out there and try and trick your mind, thinking it’s not going to happen.”

Strasburg threw five more fastballs, all of them hovering between 93 and 95. After several pitches, Strasburg had appeared to roll his right shoulder and grimace. McCann would ground out, and then Strasburg struck out Uggla with a curveball to end the inning.

“He was wiggling,” catcher Kurt Suzuki said. “I had to double-pump like every pitch because I couldn’t throw the ball back to him. So you knew something was physically wrong with him.”

In the dugout, Johnson, pitching coach Steve McCatty and trainer Lee Kuntz approached. Strasburg wanted to pitch, but Johnson would not allow it.

“There’s a lot of times you go out there and you don’t feel 100 percent,” Strasburg said. “You just go out there and gut through it. It was tough, because he kind of had his mind made up. As much as I was saying, as much as I was trying to convince him, he didn’t want me to go out there.”

Strasburg’s injury adds to a calamitous first third of the season for the Nationals. “May,” Span said, “was a disaster.” They sat at 27-27 entering the weekend and have played chunks of the year without Harper (who missed his fifth straight game Friday night), Jayson Werth, Ryan Zimmerman, Wilson Ramos and Ross Detwiler, who has been on the DL since May 16 with an oblique strain and will miss his turn again Sunday.

The Nationals have closely monitored Strasburg’s health since they drafted him with the first overall pick in 2009. Strasburg underwent Tommy John elbow ligament replacement surgery during his rookie year in 2010. Last season, General Manager Mike Rizzo controversially shut down Strasburg in September as the Nationals headed into the playoffs.

Entering Friday, Strasburg had reeled off one of the best stretches of his career. He twice pitched eight innings - which he had never previously done - and allowed three earned runs in 23 innings across three starts. In those three outings, as his season ERA lowered to 2.49, he threw 117, 108 and 112 pitches.