Gio Gonzalez bumps fists with Manager Matt Williams after throwing six scoreless innings against Miami. (John McDonnell/The Washington Post)

Gio Gonzalez left himself little room to improve after his first two seasons with the Washington Nationals. He mixed consistency with frequent excellence last year, and still it seemed bland compared to his maiden season, when he won 21 games and finished third in the Cy Young vote. He made dominance boring. “It’s been the same,” Gonzalez said. “I’ve been the same guy for years.”

This season, with the help of his new catcher, Gonzalez has found a small-yet-effective way to be different, an improvement he showcased during six breezy, scoreless innings Tuesday night in the Nationals’ 5-0 victory over the Miami Marlins at Nationals Park. Gonzalez yielded three hits, all singles, and allowed only one runner to reach second. He retired the final 10 batters he faced, struck out five and walked two.

Gonzalez has always been able to overwhelm batters with his fastball and curve. Tuesday, echoing his first start in New York, Gonzalez baffled the Marlins by throwing more change-ups than in the past. Catcher Jose Lobaton, acquired in a February trade and pressed into starting duty after Wilson Ramos broke his hand, prompted the change this spring.

“If you’ve got a third pitch working,” Lobaton said, “it’s going to be fun.”

The Nationals’ offense backed Gonzalez. Adam LaRoche went 3 for 3 with a walk and scored two runs. Anthony Rendon 2 for 4 went with three RBI and a game-sealing, two-run double in the eighth inning. Slumping Bryce Harper sparked a two-run, sixth-inning rally with a single. The Nationals doubled down, this time with success, on the risk-taking base running Manager Matt Williams promotes.

The Marlins entered Tuesday scoring six runs per game, best in the major leagues. Gonzalez shut them down. He fired 93-mph fastballs and slung biting curveballs. The biggest difference in his arsenal from last season is an improved change-up, which he has thrown more often, to great effect.

After he arrived from the Tampa Bay Rays, Lobaton made it his mission to learn every pitcher on the Nationals’ staff. Pitching coach Steve McCatty told him Gonzalez’s change-up was his third-best pitch. Once he caught Gonzalez in three or four spring starts, the designation didn’t make sense to him. Lobaton gave Gonzalez a different perspective. His change-up shouldn’t be an afterthought. It should be a feature. “We’re going to use it any count,” Lobaton told him. “Whatever happens, happens.”

Last year, Gonzalez threw his change-up once every 10 pitches, and he threw more than 16.8 percent change-ups in only one start, an outing in May against the Pittsburgh Pirates. In his first start this season, Gonzalez threw 18 change-ups in 91 pitches. Tuesday night, Gonzalez twirled 16 in 101 pitches. In total, 17.7 percent of his pitches this season have been change-ups.

The difference has helped him dominate. In his first two starts, Gonzalez has allowed one run in 12 innings while striking out 11, yielding six hits and walking three. The change-up works on its own, but it makes his electric fastball-curve combo more devastating.

“If that change-up works, the curveball and fastball are going to be awesome,” Lobaton said. “He throws 93, 94. The fastball is going to look like 95, 96.”

In the second inning, after Garrett Jones led off with a bunt single through a gap in the Nationals’ infield shift, Gonzalez fell behind Jarrod Saltalamacchia with a first-pitch fastball. Gonzalez then threw Saltalamacchia three consecutive change-ups. He swung and missed at all three.

“He’s not afraid to throw anything,” Lobaton said. “Today, I saw the change-up working with the curveball. I said, ‘Any count, I’m going to call it.’ “

The Nationals’ offense provided plenty of help. With two outs in the first, Jayson Werth scalded a double to the left-center field gap. LaRoche followed with a soft liner to left field, scoring Werth and giving the Nationals a 1-0 lead.

The Nationals were still clinging to that margin with one out in the sixth when Harper came to the plate, 0 for 2 in the game and stuck in a 3-for-23 rut for the season. After he chucked equipment at various times and declared himself “lost” Saturday night, Williams gave him Sunday off in order to clear his mind. Harper said he would watch old video of himself and call his father. At least for one at-bat, it worked — Harper laced a single to left.

Prior to the game, Williams had alerted the Nationals to Marlins starter Henderson Alvarez’s propensity to throw curveballs in the dirt. It is a strength — he often tricks hitters into chasing. But it also leaves him open to giving away extra bases.

“He’s not a guy you can steal a lot of bases on,” Williams said. “But he does throw a lot of balls in the dirt, so that’s something we talked about.”

As Ian Desmond batted, an Alvarez slider squirted a few feet away from catcher Jarrod Saltalamacchia. LaRoche, who had singled two batters after Harper, was ready. As Saltalamacchia searched for the ball, LaRoche lumbered to second.

In the Nationals’ home opener, LaRoche had been thrown out at home, and yet afterward he extolled Williams’s preference for aggressive base running. Force the defense to make plays, he said, and eventually it would pay dividends.

Now, Saltalamacchia fired a strike. As LaRoche slid into Jeff Baker’s tag, it seemed he had again run the Nationals out of an inning. But aggression won: LaRoche’s headfirst dive jarred the ball loose and Harper scored from third.

“We have to make sure that we take advantage of those opportunities,” Williams said.

After Desmond walked, Rendon smoked a single to center and scored LaRoche to put the Nationals ahead, 3-0. Rendon effectively ended the game in the eighth, when he smashed a two-run double off the left field fence. The Nationals had extended their lead to five, far more runs than Gonzalez needed. LaRoche scored from first, and by that time he had tired of so much running.

“Way to swing it,” LaRoche told Rendon. “Next time, put that ball in the seats.”