PHOENIX — Joe Ross was an out from finishing the fourth — and so close to saving a tattered outing — when his command slipped, starting with a fastball way down and in.

It hit Pavin Smith, the Arizona Diamondbacks’ leadoff batter, and stirred the backbreaking rally Saturday night. Next Ross walked Josh Rojas on five pitches, missed well high to Eduardo Escobar and called Yan Gomes, his catcher, to the mound. Pitching coach Jim Hickey jogged out from the dugout. The infield surrounded Ross. But five pitches later, after Escobar had scorched a foul ball, and when it was clear Ross had lost his feel, Escobar pulled a dead-center fastball for a three-run homer.

“Keep it up and away, four seam,” Ross said of what Escobar sent over the right field wall. “I threw some okay ones. But that one might have been … I didn’t really look at it yet … just got a little too much of the plate, which was the case with a few fastballs today.”

That swing and that pitch, and the two at-bats before it, buried the Washington Nationals in an 11-4 defeat to the Diamondbacks at Chase Field. Ross lasted four innings (plus two batters) and was charged with eight earned runs on eight hits and three walks. The two extra batters came once Manager Dave Martinez pushed him to the fifth, despite Ross leading off the top half, an easy spot to lift a struggling starter.

And both reached, on a single and a walk, before Ross was hooked for reliever Sam Clay. And both scored, too, on Clay’s wild pitch and a single from pinch-hitter Andrew Young. Washington’s offense registered three hits in the first two innings and none between the third and sixth. It was a sharp contrast to blowing out the Diamondbacks, 17-2, in the series opener Friday. The Nationals dropped to 15-20, while the Diamondbacks improved to 18-22.

“He tried to battle there, he made a good pitch to Escobar, we didn’t get it and the next pitch was basically right down the middle,” Martinez said of Ross. “We tried to stretch him out for another inning, just to kind of save our bullpen down four, but at that point I saw his velo going down and I just wanted to get him out of there.”

After his previous three outings, despite lines that looked fine on paper, Ross had the same assessment: He had figured it out without his best command. At times, he got by with far less than that. His sinker was too often too high in the zone. His slider was inconsistent. But he had held opponents to two or fewer runs in every outing but April 19, when the St. Louis Cardinals rocked him for 10 in 4⅓ innings. He and the Nationals could appreciate that.

Then the Diamondbacks full-on blitzed him Saturday. The lack of command caught up. By Ross’s 10th pitch, their first four batters — Smith, Rojas, Escobar and David Peralta — had collected a hit. Rojas belted an inside slider for a double off the right field wall. Escobar, who also homered off Austin Voth in the eighth, finishing with seven RBI, first punched a two-run single to erase the Nationals’ 1-0 lead. Peralta scored once Daulton Varsho ripped a single up the middle. Ross only escaped the jam when Seth Frankoff, the Diamondbacks’ starter, tapped out to third.

Frankoff, 32, was making his fourth career appearance and first career start. That was the product of Arizona’s banged-up staff. But the Nationals didn’t quite capitalize on his early lack of control. He fired two wild pitches in the first, then stranded Josh Harrison on third by retiring Kyle Schwarber (via strikeout) and Starlin Castro (who rolled a grounder to the left side). In the second, after Victor Robles singled in Josh Bell and stole second, Trea Turner left him there with a looking strikeout. And Ross needed a lot of run support.

Ross settled in for the second and third, discarding six of seven Diamondbacks. The fourth was going well after back-to-back strikeouts of Nick Heath and Frankoff. In all, when his evening was through, he had thrown a good amount of strikes and was burned on a handful of misplaced pitches. He got a lot more called strikes than whiffs from the swing-happy Diamondbacks. But the trouble really began when, behind 2-1, he plunked Smith with that errant fastball.

“Just a little mental frustration,” Ross said of the mistakes that followed the hit by pitch. “ … Tried to go fastball in and just yanked it. I don’t know the last time I’ve really done that with a heater like that.”

His pitches were tugged from the zone and few returned. The exception, of course, was the one Escobar used to turn a 3-2 advantage into a commanding 6-2 Arizona lead. Ross would end the fourth at 80 pitches. Clay had warmed during the inning and could have replaced him once a pinch hitter did. But Martinez kept him in to bat, he reached on an error and was kept on third when Schwarber, who stranded eight batters in an 0-for-5 game, struck out with the bases loaded. Then Ross was tagged with a single, walked Varsho and exited after throwing six more balls toward the plate.

Only half of them were particularly close. The rest were a sound description of his night.