NEW YORK -- One storyline in a juicy pitching matchup between Washington right-hander Stephen Strasburg and New York Mets right-hander Noah Syndergaard disappeared hours before first pitch Friday night, when the Nationals announced Strasburg would not start or pitch for the National League in next Tuesday's All-Star Game.

Unfortunately for the Mets, another storyline developed hours later, when Strasburg continued to pitch like an All-Star Game starter while Syndergaard all but ensured he would not be able to start or pitch next Tuesday.

Syndergaard left due to arm fatigue in the fifth inning Friday night, when Strasburg completed his unbeaten first half by allowing one run and two hits over seven strong innings as he earned the win in the Nationals' 3-1 victory at Citi Field.

Strasburg (12-0, 2.62 ERA) is the first National League pitcher to win at least his first 12 decisions in a season since Rube Marquard won his first 18 decisions for the New York Giants in 1912.

"Just shows how good they swing on the days I pitch, I guess," the usually stoic Strasburg said with a rare laugh. "I don't know I'm just trying to do my part, keep it close and give the guys an opportunity to win."

Strasburg is also the first pitcher to reach the All-Star Break with double-digit wins and no losses since Dave McNally was 13-0 prior to the All-Star Game for the Baltimore Orioles in 1969.

"That's pretty good company," Nationals manager Dusty Baker said.

Strasburg will keep company with his fellow All-Stars in San Diego, where he will partake in the festivities despite not pitching. He said after the game that a recent stint on the disabled list due to an upper-back injury played into his decision not to argue with the Nationals' recommendation that he sit out the game.

"They came to me and they said that that was what they were thinking," Strasburg said. "In my head, I'm like 'I want to make up the two starts I missed.' So hopefully (he'll) be able to start the first game back and get the second half going right."

Strasburg ended the first half going in the right direction. After throwing 6 2/3 no-hit innings in his first start back from the disabled list Sunday, he opened Friday night with four no-hit innings before giving up a homer to Asdrubal Cabrera leading off the fifth.

Brandon Nimmo followed with a single before Strasburg retired nine of the final 10 batters he faced. He walked three and struck out nine.

Shawn Kelley gave up two hits to start the eighth, but Oliver Perez and Blake Treinen wriggled out of the jam before Jonathan Papelbon (18th save) threw a perfect ninth inning.

Clint Robinson hit a two-run homer in the second while Daniel Murphy laced an RBI double in the third for the Nationals (52-36), who extended their NL East lead over the second-place Mets (47-39) to four games.

While Strasburg looks to be in line to start the Nationals' first game of the second half, Syndergaard's post-All-Star Game availability decidedly murkier. He left after 4 2/3 innings Friday, when his final two pitches -- a pair of low 90 mph fastballs to Jayson Werth -- spooked Werth as well as Mets manager Terry Collins.

"The first pitch, it didn't come out the same," Werth said. "I thought maybe it was a slider that he didn't finish or something right. I saw the 93 and that's a little bit harder than his slider. So it was kind of just a weird pitch. I took it and then he threw another one about the same speed. I was kind of baffled a little bit because it wasn't like anything else I had ever seen from him."

Said Collins: "I said 'I don't like the looks of this.' And (Syndergaard) just said 'I lost it' and he just said his arm is tired. So we took him out."

Syndergaard, who fell to 9-4 as his ERA rose to 2.56 after he gave up the three runs on four hits and three walks while striking out five, has undergone two known elbow exams this season and has been pitching through a bone chip in his elbow. Syndergaard and Collins said that Friday's issue is not believed to be connected.

"There's no pain, there's no discomfort in my elbow regarding the bone spur or anything," Syndergaard said. "It all boils down to a little shoulder fatigue."

Collins said " ... that's a pretty good assumption" when asked if Syndergaard and outfielder Yoenis Cespedes -- who exited after the third inning with a sore right quad -- would not play in the All-Star Game.

The injuries to Cespedes and Syndergaard came hours after the Mets announced Opening Day starter Matt Harvey will undergo season-ending surgery to repair thoracic outlet syndrome.

NOTES: Rain delayed the first pitch by 37 minutes. ... The Nationals recalled OF Michael Taylor and INF Trea Turner from Triple-A Syracuse, placed 1B Ryan Zimmerman (right rib cage strain) on the 15-day disabled list and optioned RHP Lucas Giolito to Syracuse. ... Mets RHP Bartolo Colon and Nationals RHP Max Scherzer were added to the National League All-Star team. The 43-year-old Colon, the oldest player in baseball, will be the oldest All-Star since former Yankees RHP Mariano Rivera made the American League team in 2013. Scherzer replaces his teammate, RHP Stephen Strasburg.