Stephen Strasburg picks up his first win of the year. (Adam Hunger/Reuters)

The delicate treatment of Stephen Strasburg ended Wednesday afternoon. In the sixth inning, with the tying run on second base, the Washington Nationals chose competition over precaution. There was no other pitcher they wanted on the mound, and so, even as Strasburg crossed a new threshold, the Nationals left him out there.

As his pitch count surpassed 100 for the first time as a professional, Strasburg handled the most crucial moment of the Nationals’ 4-0 victory over the New York Mets himself. With his 107th pitch, Strasburg struck out Jason Bay with a fastball over the outside corner. With his 108th, Josh Thole ended the rally with a flyball to left field. Strasburg walked off the mound. Two base runners skulked off the field. The bullpen gate stayed shut.

“He’s just one of the guys now,” Manager Davey Johnson said. “I’m going to handle him just like he’s perfectly healthy, and he had plenty left in the tank there.”

After Strasburg lifted them to a second series victory, the Nationals head home tied for first place at 4-2 entering Thursday’s Nationals Park opener against the Cincinnati Reds. On a brisk, gray day before 34,614 at Citi Field, in his 19th major league start, Strasburg had finished one of the most dominant performances of his young career.

Strasburg struck out nine in six scoreless innings, allowing two singles and three walks as he outdueled and outlasted Mets ace Johan Santana. Strasburg overcame early wildness (and a disagreement with home plate umpire Larry Vanover) to at one point retire 10 batters in a row, overpowering the Mets with a heavy dose of curveballs and change-ups.

“By no means in the back of my head was I thinking, ‘How many pitches am I at?’ ” Strasburg said.

With Strasburg 19 months removed from Tommy John surgery, the Nationals tested his durability like never before, and it did not concern them in the least.

“It didn’t really cross my mind,” pitching coach Steve McCatty said. “When he got over 100 pitches, I knew we were going to get, ‘Oh, it’s the miracle, he crossed the finish line.’ It’s not. You throw your pitches. He’s healthy.”

Strasburg threw 100 pitches frequently in college at San Diego State, but as a professional he topped out at 99 on July 16, 2010, one month and five days before he tore his ulnar collateral ligament. With Jim Riggleman as manager, the Nationals prioritized protecting Strasburg and, perhaps more, their own liability.

“Let’s put it this way: There’s a different way the manager is managing the game, too,” McCatty said. “I’m not saying that Riggleman is wrong. Hey, I believe the pitcher has got to throw pitches. . . . When you sit there and watch him throw, you don’t look at the mark of 100. You see what you see — he was throwing pretty good — and that’s what Davey does.”

The Nationals sent Strasburg to the mound for the sixth inning having thrown 84 pitches, clinging to a 1-0 lead. Daniel Murphy’s seven-pitch at-bat ended with a flyout to left field. The Nationals’ bullpen still hadn’t stirred.

After Lucas Duda walked on five pitches, McCatty called the bullpen, and Sean Burnett heated up. Ike Davis lined Strasburg’s 102nd pitch into right field for a single. With a man on second and one out, Strasburg had taken ownership of whether the Nationals would stay ahead or fall behind.

“I’d have probably had to strangle him to get hold of the ball to get it out of his hand,” Johnson said. “I didn’t want to fight him on the mound.”

Said Strasburg: “You don’t want to get taken out in the middle of an inning and not being able to finish it. You don’t want to go 51 / 3 innings. You want to go six.”

As Bay walked to the plate, McCatty ambled to the mound to calm Strasburg. “Remember, just trust your stuff out there,” McCatty told him. “Pitch to contact. You’re one pitch away.”

Strasburg worked the count to 2-2 and then rifled a 95 mph two-seamer over the outside corner, perhaps off. Vanover pumped his fists, strike three. After Bay protested, Thole lifted a lazy fly to left.

“His stuff is overpowering enough that even if he does get behind, he can still get outs,” Bay said. “That’s how he separates himself from a lot of other guys.”

Strasburg had stranded two runners and proven another facet of his arm strength. The Nationals had shown Strasburg — and his teammates — they will let him finish.

“It’s huge,” left fielder Mark DeRosa said. “We have confidence in every guy in the clubhouse and in that bullpen. At the same time, when he’s on the mound, when he’s lighting it up the way he can — he’s got a Bugs Bunny curveball, the change-up is working — you know those guys don’t want to face that.”

Once the Nationals tacked on three runs and the bullpen preserved the shutout, Strasburg could savor a hard-earned win. Back in the first, he thought he had struck out leadoff hitter Ruben Tejada with a 2-2 fastball. He barked at Vanover for calling it a ball. Tejada roped a single into center on the next pitch.

“He still gets frustrated over certain things, maybe a call that he thinks is a strike,” McCatty said. “He can’t worry about it. Get past it. You’re not going to get it back by yelling at him, asking him questions.”

Still irritated, Strasburg walked Murphy. After a wild pitch, runners stood on second and third with one out, and then Strasburg ran the count to 3-1 on Davis.

“I was trying to calm him down,” Flores said. “The umpire was not really giving him strikes. We tried to look for another way to come back, and he made the adjustment.”

Strasburg snapped out of it. He threw a 3-1 change-up Davis could not have hit with a canoe paddle. He backed that up with a 3-2 curveball that started on the outside edge of the plate and broke to the inside corner. Never expecting a curve on 3-2, and probably not equipped to handle one like that in any count, Davis watched it for strike three.

Strasburg never looked back. He walked Thole to start the second but retired 13 of the next 14 batters he faced, striking out seven of them. Strasburg turned to his change-up, throwing 24 of them, more than triple what he threw opening day.

“Honestly,” Strasburg said, “I think I have four out pitches.”

Washington will see them again soon. Strasburg will make his 2012 home unveiling Monday night. Until then, the Nationals Park crowds can watch a first-place team with an ace who could throw 100 pitches and not even think about it.