Edwin Jackson leads the Nationals pitching staff in innings and pitched into the ninth Monday night. (Frank Gunn/ASSOCIATED PRESS)

After he had put in another hard, full day’s work, Edwin Jackson glanced around the Washington Nationals’ clubhouse Monday night and shook his head, more out of relief than jubilation. “Just trying to keep up with the young guns,” he said.

Jackson had lifted the Nationals to a 6-3 victory over the Toronto Blue Jays by pitching into the ninth inning, allowing two runs on three hits to continue his season as an elite pitcher trapped in a fourth-starter’s role. The Rogers Centre crowd focused its attention on Bryce Harper, who delivered another performance that defied his 19 years, going 3 for 4 with a walk and two runs.

This season, Jackson has become accustomed to being overlooked. The firepower at the top of the Nationals’ rotation, the youthful brilliance of Stephen Strasburg and Gio Gonzalez, often overshadows Jackson. But Jackson, 28, with his 3.02 ERA and plowhorse attitude, has kept the pace, undaunted by the performances ahead of him in the majors’ best rotation.

“I think if anything, it pushes him,” said first baseman Adam LaRoche, who smashed a two-run homer into the upper deck. “These guys compete against each other. They know what the other ones are doing. They feed off that.”

Jackson’s start followed Strasburg, Gonzalez and Jordan Zimmermann each allowing three earned runs or fewer in at least six innings. The Nationals have won all four games, and six of their past seven. With the Atlanta Braves’ loss to the New York Yankees, the Nationals surged into first place by three games, their largest lead of the season, even with Ryan Zimmerman and Michael Morse yet to find their form.

“I don’t think we’re super-hot,” shortstop Ian Desmond said. “When we get super-hot, it’s going to be really fun.”

It is hard to fathom now: If the Nationals’ season had unfolded how they expected, Harper would still be a minor leaguer. The Nationals planned to give Harper at least 250 plate appearances before they summoned him to the majors. He had 82 at Class AAA Syracuse before injuries made him the chosen contingency plan. He has taken 168 as a major leaguer — a total of 250, right at his intended target.

“He’s not going back,” Manager Davey Johnson said, laughing at the obviousness of the statement. Harper leads the Nationals in batting average (.295) on-base percentage (.381) and slugging (.527) since his call-up.

“You just have to stay even-keel,” Harper said. “I went 3 for 4 today. I could go 0 for 4 tomorrow.”

All through the night, the crowd in right field serenaded him with, “Haaaar-Perrr.” He did not react, but he noticed. Johnson moved Harper from right field at the start of the game to center. Later, he told Harper he’d be moving back to right. “I haven’t made friends with all those people in center yet,” Harper replied, smiling.

Monday night, Harper’s performance bulwarked another workhorse outing from Jackson. He came off the mound in the eighth inning, having allowed no runs since the first inning. He told Johnson, “Give me one batter. I want to finish it.” No other Nationals starter had pitched into the ninth inning all year. Jackson wanted his second complete game.

“I feel like I’m the one whose job it is in the rotation to go out there and eat innings,” Jackson said. “I can sacrifice personal numbers to go out and help the team.”

Jackson knew he would be done if any Blue Jay reached base. Edwin Encarnacion led off with a double, and Jackson was done after 108 pitches. Encarnacion would scored after Yan Gomes hit a cosmetic home run off Sean Burnett. Jackson’s ERA nudged back over 3.00, a run that he would not have allowed if he took his eight innings and hit the showers.

“He’s such a good teammate, because he wants to go out in the ninth and protect the bullpen,” Desmond said.

Jackson has produced more quality in his quantity than the Nationals could have expected. He has perhaps been the Nationals’ best starter for almost a month. In his past five starts, Jackson has a 2.21 ERA. The Nationals signed Jackson to his one-year, $11 million deal to devour innings. He leads them with 80 1 / 3 innings, but Jackson also has career bests in walks per nine innings (2.5) hits per nine (6.5) and ERA (3.02).

The key has been his efficiency. Jackson entered the game with the fewest pitches per inning of any major league starter. Colby Rasmus, the second batter of the game, launched a home run into the upper deck. Jackson needed 24 pitches to escape the inning. Still, “I didn’t feel like I was erratic,” Jackson said.

Jackson needed only 40 pitches to get through the next four innings. At one point, he retired nine consecutive batters. Strasburg’s overwhelming velocity and Gonzalez’s preposterous curveball make you forget Jackson’s gifts — a 95-mph fastball and a hard, biting slider that dips straight down.

“He’s been dominant,” Johnson said.

The Nationals scored all the runs they needed after an unexpected break in the first inning. After Steve Lombardozzi led off the game with a double to right field, Blue Jays starter Brandon Morrow threw Harper a cutter low to make the count 2-1. He then walked off the mound with a left oblique strain, done for the night nine pitches into the game.

Toronto swapped Morrow, who led their staff with a 2.90 ERA, for Chad Beck, a 27-year-old with four major league innings to his name. Beck confronted a rugged surprise assignment: Harper stood at the plate with no outs, a man on second base and the count already in his favor.

“That’s never happened to me before,” Harper said.

Beck began with a 93-mph low fastball. Harper smoked a groundball that hopped through the right side. Lombardozzi charged home and slid in just before Jose Bautista’s throw arrived at the plate, giving the Nationals a 1-0 lead.

In the third inning, LaRoche crushed a hanging slider several rows into the upper deck in right field, his team-leading 11th homer of the season. “I hit that one pretty good,” he said. “That’s a pitch, a very hittable slider, that I’ve been pulling foul. I’m glad I made the adjustment.” Rick Ankiel would add a home run in the eighth, a capper to their 14-hit outburst.

They did not need nearly that many runs for a starter who calls himself “a young veteran.” As Jackson lamented his need to keep up, reliever Michael Gonzalez strode by and corrected him. “No man,” he said. “You’re showing them how it’s done.”