Nationals starter Jordan Zimmermann, backed by a strong outing from his bullpen, beats the Mets in their 2011 home opener at Citi Field. (CHRIS TROTMAN/GETTY IMAGES)

Jordan Zimmermann emerged one last time from the Citi Field visitors’ dugout, the afternoon having turned to evening and his right arm already tested more than it had been, on any single day, for the past 21 months. For most starters, it would have been an average day’s work. For Zimmermann, it was another milepost in his comeback from Tommy John surgery.

The most crucial moments during the Nationals’ 6-2 victory Friday over the New York Mets would come later, when Tyler Clippard cleaned house again and Ivan Rodriguez delivered a knockout blow with his first hit of the season. But the most significant moment for the Nationals’ franchise happened in the bottom of the sixth, when Zimmerman simply climbed the dugout steps. He had thrown 91 pitches, and the Nationals were sending him back out.

“I wasn’t tired at all,” Zimmermann said. “I felt good all day.”

That Zimmermann can say that should make Nationals executives exchange high-fives and toast drinks. Zimmermann would record only one more out and toss just eight more pitches, ending a start in which he allowed two runs on six hits and no walks before 41,075. The results were good enough to ruin the Mets’ home opener and get the Nationals even with the Mets in the standings, both teams now 3-4. But Zimmermann’s numbers were not as meaningful as the sheer workload.

Zimmermann had not thrown more than 86 pitches in a game since July 18, 2009. He threw 100 that day in a loss to the Chicago Cubs. About a month later, he had his ulnar collateral ligament replaced and started a grueling rehab that, now more than at any other point, he can say he has placed behind him.

“It’s a big confidence builder,” Zimmermann said.

Zimmermann struck out four of the first eight batters he faced, three of them looking. He fired mid-90s four-seam fastballs at the knees and on the corners, and he fired high-80s sliders with the count full. He threw only two change-ups. “That’s how good he is,” Rodriguez said. “He’s got another pitch that we didn’t use, and he still did a tremendous job.”

Zimmermann provided his own offense, lacing one of R.A. Dickey’s knuckleballs to right for a bases-loaded, two-RBI single in the second inning. (“I don’t know what happened there,” he said.) The Nationals benefited from Dickey’s wildness, caused by a split fingernail on his right index finger. They drew five walks, which tied Dickey’s career high.

But the Nationals continued their early-season habit of wasting rallies, and they held only a 3-2 lead when the bottom of the sixth arrived. Manager Jim Riggleman approached Zimmermann in the dugout and told him he would be facing David Wright and Carlos Beltran. The Nationals have no strict pitch count for Zimmermann, but they probably will not let him throw more than six innings. Friday, they wanted to keep Zimmermann’s pitch total below 100.

“We’re trying to keep as little stress on his arm as we can,” Manager Jim Riggleman said. “Because it’s a valuable arm.”

Wright grounded to shortstop, but Beltran ended Zimmermann’s day. When he walked off the field, 99 pitches thrown, he still felt strong.

In the seventh, Chad Gaudin walked two Mets batters and watched them pushed to second and third by a sacrifice bunt. The Nationals clung to a one-run lead, and the tying run stood 90 feet from home, with the go-ahead run just behind, with only one out. Jose Reyes, one of the Mets’ most dangerous hitters, stood at the plate. Riggleman summoned Clippard.

“When we need a strikeout,” Riggleman said, “he’s the guy.”

And, Friday, he was again. Entering Friday, Reyes had seen 109 pitches this year and swung and missed at five. Clippard threw Reyes five pitches. He swung and missed at two, the first and last. They were both 80-mph change-ups that, because of Clippard’s funky delivery, look to a batter like an optical illusion.

“I was thinking strikeout,” Rodriguez said. “In that situation, you have to work him to try to strike out him. The way he pitched Reyes was unbelievable. Those two or three change-ups that we threw to him was nasty.”

“You don’t really want to go into an at-bat thinking you’re going to strike a guy out,” Clippard said. “Strikeouts aren’t easy in this league.”

After Clippard ended the inning with a bouncer from Angel Pagan, he smacked the inside of his glove with his fist. Over two days, he had pitched 22 / 3 innings, struck out four of the eight batters he faced and thrown 26 of 30 pitches for strikes.

The Nationals needed no more high-wire acts from their relievers. In the eighth, Rodriguez came to the plate with the Nationals still up one and with his swing out of whack. Rodriguez had hit one ball out of the infield in 12 at-bats. His previous two trips resulted in a fielder’s choice that got a runner thrown out at home and a 4-6-3 double play.

“I’ve been too quick, just hitting on top of the ball,” Rodriguez said. Against hard-throwing right-hander Bobby Parnell, Rodriguez shot a single to right, scoring two and putting the Nationals ahead, 5-2.

“I know I’m going to get my hits,” Rodriguez said. “That’s baseball. You cannot be frustrated. Why am I going to be frustrated at this part of my career? I’m a hard worker. I know I’m going to my hits.”