Danny Espinosa was 1 for 18 against Mets knuckleballer R.A. Dickey before lacing an RBI double down the third base line in the third inning. Espinosa (2 for 4) would later score. (Kathy Kmonicek/Associated Press)

Gio Gonzalez had not given the Washington Nationals reason to worry before Tuesday night, but he had been veering toward that direction. They never doubted their left-handed, ever-smiling all-star, but Gonzalez had fallen off the pace that made him an early-season Cy Young candidate. His relative slide culminated last week, when he allowed the New York Mets six runs in less than four innings.

Five days later, against the same New York Mets, Gonzalez delivered a gem, one of the best starts of a season whose game log reads like a greatest hits collection. In a 5-2 victory at Citi Field, Gonzalez allowed no earned runs in seven efficient, dominant innings. He yielded two hits, walked two and threw only 87 pitches. The performance put to rest any worries and smothered any doubts.

“They roughed him up over at our place, but he pitched a masterpiece,” Manager Davey Johnson said. “He was dominant from the first pitch on. He had something to prove, and he was going to prove it.”

Gonzalez earned his 13th win, which tied him for the National League lead with R.A. Dickey, the knuckleballer he opposed Tuesday night for the second time in a week. Dickey, who easily won last Thursday’s encounter, beguiled the Nationals until the sixth inning, when they exploded for four runs, all of them with two outs. Ryan Zimmerman added to his incredible run with three more hits, Adam LaRoche smashed an upper-deck homer and Danny Espinosa stayed hot in the second half with two hits.

Gonzalez, who entered with a 4.93 ERA in his past nine starts, returned to his earlier dominance, but in a different way. Before Tuesday’s game, he and catcher Jesus Flores resolved to throw more strikes against the Mets, a lineup of patient hitters. They would lean on his sinker more than his off-speed pitches. “We talked about being more aggressive in the zone and attacking the hitters,” Flores said.

Gonzalez did not rack up strikeouts — he had four, a thimbleful for a pitcher averaging 10.5 per nine innings. He instead pumped strikes and induced contact early in counts. He threw six pitches in the first and five in the fourth. After four innings, he had thrown a scant 39.

“I wanted to redeem myself from my last start, give our team a chance to go out there and try to compete,” Gonzalez said. “You want to bounce back as a pitcher. You don’t want to feel down and out.

But he still trailed. The Mets scored an unearned run in the second inning after Espinosa made a throw from shortstop that just pulled LaRoche off the bag at first, enough to allow Scott Hairston to reach. Hairston stole second, then scored when Ronny Cedeno singled to right. Bryce Harper at least ended the inning with an outfield assist, cutting down Cedeno at second.

The Nationals tied it in the fourth. Zimmerman flared a ground-rule double into right field, the ball bouncing sideways into the seats along the foul line. When Espinosa walked into the batter’s box, he stood 1 for 18 against Dickey in his career. Espinosa prides himself on playing every day, but last year he gladly sat out against Dickey because he believed facing him would distort the timing of his swing for days to come.

Batting right-handed on Tuesday night, Espinosa turned the tables. He yanked a sharp grounder down the third base line and into the corner for an RBI double. The Nationals had made it 1-1.

The game churned along as a stalemate, both Dickey and Gonzalez dealing. Dickey struck out Harper three times, dropping him to 0 for 10 with six strikeouts in his rookie season against the knuckleballer.

In the sixth, another lazy inning suddenly turned into an outburst . With two outs, Michael Morse ripped a single to left field. LaRoche walked to the plate carrying Roger Bernadina’s bat, a ploy to help him against Dickey’s knuckleball. Ian Desmond, along for the trip as he heals a strained oblique muscle, suggested LaRoche use Bernadina’s lumber, which is a couple ounces lighter than LaRoche’s 33-ounce model.

“Which sounds like nothing, but when you’re holding them every day, you can definitely tell the difference,” LaRoche said. “Take the lighter bat up there and you’ll have a chance to move it a little bit as the pitch is coming, is what the theory was. So I bought into it.”

LaRoche started his at-bat by fouling off a fastball, then found a lifeless knuckleball that stayed still, like dust in a spotlight. He hammered it to right field, about eight rows into the upper deck.

“You just hope when you swing your bat’s in the right spot,” LaRoche said. “That was kind of the theory behind the light bat, have a little more control over it. Whether it’s true or not . . . it worked once.”

The Nationals led 3-1, and they weren’t done. Espinosa ripped another single, this one to right field. Bernadina dribbled a knuckleball down the first base, a perfect unintentional bunt — Ike Davis scooped the ball, but Bernadina raced by him before Davis could tag him.

Flores, scuffling for the past month, provided one more crucial hit, a single to left. Espinosa scored from second, and Jason Bay’s poor throw allowed Bernadina to score from first. In a flash, the Nationals (57-39) had turned a pitcher’s duel into a 5-1 breeze.

Gonzalez protected his large lead for two more innings, allowing a single and a walk in the seventh. Despite Gonzalez’s low pitch count, Johnson pulled him for pinch hitter Tyler Moore in the top of the eighth. Johnson would have sent Gonzalez back for the eighth if his spot in the lineup had not come up.

“He wasn’t too hard on me,” Johnson said. “He did come up to me said, ‘Well, you can still shake my hand.’ But what a great game. And a great comeback.”