Bud Black’s argument with umpire Gary Darling earned the Padres Manager an ejection in the sixth inning Tuesday night in San Diego. (Denis Poroy/Getty Images)

While their best player visited the doctor and their offense remained absent, the Washington Nationals’ starting rotation again made anything seem possible. Ryan Zimmerman can flirt with the disabled list, and their starting eight position players can scrape together two hits. Send Gio Gonzalez to the mound, and nothing else matters.

Tuesday night, while Zimmerman received an MRI that returned unfavorable results, Gonzalez delivered another dazzling start in a 3-1 victory over the San Diego Padres before 16,599 at Petco Park. Gonzalez fired six shutout innings, running his personal scoreless streak to 20 innings and lowering his ERA to 1.52. Gonzalez allowed two hits, increasing his total over his 20 innings of zeros to a scant six.

Gonzalez out-dueled left-hander Clayton Richard, who held the Nationals hitless for four innings and scoreless for six. They finally broke through in the seventh, when Chad Tracy reprised his season-opening role as an off-the-bench hero with a two-run, pinch-hit single.

“We got to scratch and claw to try to get a get a couple runs,” Manager Davey Johnson said. “We’ve got to be perfect with our pitching.”

So far, their pitching has tested the limits of how feeble a staff can make major league hitters. They own a 2.21 ERA, including a 1.72 ERA among their starting five. Moments after Henry Rodriguez pumped 100-mile-per-hour fastballs and mind-bending, high-80s changeups in the ninth to polish off his fifth save, the Atlanta Braves beat the Los Angeles Dodgers, 4-3 — a result that gave the Nationals, at 13-4, the best record in the National League.

“It’s exciting, because we as players were talking about it, we’re not really firing on all cylinders right now,” reliever Tyler Clippard said. “But we’re 13-4. We’ve got a lot of the pieces in place, and we’re going to start swinging it eventually. If we go through our lulls, we can pitch our way through them. That’s the exciting thing about this club.”

The Nationals possess an impotent offense and a crowded trainer’s room, but their rotation covers up those and any other ills. After Gonzalez’s latest tour de force, Nationals starters have thrown 22 consecutive scoreless innings, which is only their second longest such streak this season; they had a 23-inning scoreless streak, too. In 13 of 17 games, the Nationals’ starters have allowed two or fewer earned runs.

And yet, their offense makes them sweat it out, night after night. Richard matched Gonzalez zero for zero until the sixth, when the Nationals finally broke through. Xavier Nady scalded a double to left field, only the second hit off Richard all night. Wilson Ramos drew a walk, and Steve Lombardozzi bunted both runners into scoring position.

With his spot in order due up, Gonzalez’s night had ended after 91 pitches. “He had a lot more left in him,” Johnson said, but one byproduct of a crummy offense is pulling the starter sooner than you’d like. The Nationals obviously needed a pinch hitter, but who?

With Zimmerman out and Richard starting, his usual right-handed pinch-hitting candidates — Nady, Mark DeRosa and Lombardozzi — were already in the game. Johnson, not wanting to burn backup catcher Jesus Flores so early, had no choice but to send up a lefty.

Tracy and Rick Ankiel had discussed the scenario, and they knew one of them could be tabbed for the unusual task, a left-handed pinch-hitter against a lefty starter. In the tunnel behind their dugout, they took “flips” — short, hard throws in the batting cage — from Ali Modami, their left-handed batting practice pitcher.

Tracy had delivered clutch pinch-hits in the Nationals’ first two games of the season, but was hitless in his 11 at-bats since. But he had hit the ball hard, and Johnson wanted him at the plate. Before Tracy walked to the on-deck circle, Gonzalez approached him in the dugout and said, “I have 100 percent confidence that you’re going to get the job done.”

“I think Davey knows how hard it is to go up there and pinch hit,” Tracy said. “We’re veteran guys. We’re going to give you a good at-bat. We’re not going to be overwhelmed by anybody, or the nerves are not going to get to us.”

The infield moved in, and Tracy did not focus on any particular pitch. He just wanted to barrel the ball, hit it hard enough to get through the infield. Against Richard, Tracy took one ball, then smacked a hard groundball up the middle. Once it got past Richard, Tracy knew it would scoot into the outfield. Both Nady and Ramos raced home, giving the Nationals a 2-0 lead.

A two-run lead over the Padres at Petco Park typically ensures victory, but the Nationals forced themselves to clear one more hurdle. Craig Stammen relieved Gonzalez and, following several scintillating appearances, had nothing. He yielded a walk and a single, then exited so Clippard could clean up the mess.

Clippard could be the Nationals’ closer with Drew Storen recovering from surgery, but Johnson wanted him available for moments like this: two on, no outs and the winning run at the plate in the form of a powerful young hitter. Yonder Alonso took two vicious hacks, and Clippard struck him out with a high fastball.

But Jason Bartlett followed with a bloop single to center. Both runners moved up a base before Jayson Werth bobbled the ball trying to pick it up. The error let Cameron Maybin score and moved Orlando Hudson to third.

For the final two outs, Clippard engaged in an epic struggle. With men on second and third, Mark Kotsay fouled off nine pitches and took two balls. “Put it in play,” Clippard thought to himself before Kotsay popped up the 12th pitch Clippard threw him, an 81-mph changeup, to shortstop.

Clippard still needed to retire Chris Denorfia. He took Clippard to a 3-2 count before chopping a changeup to third base, where Zimmerman fill-in Lombardozzi made a nifty, running play to end the inning. Clippard, having thrown 26 pitches to four batters, pumped his fist.

Sunday’s rainout made Gonzalez wait six days between starts, enough time to throw off a pitcher’s carefully calibrated routine. In 13 previous career starts after at least six days of rest, Gonzalez was 5-6 with a 6.29 ERA.

After a six-pitch first inning, some rust may have shown. Gonzalez stomped off the mound after the second inning, yelling at himself and smacking his glove. He hadn’t allowed a run; he had merely walked two batters.

Gonzalez settled from there. Chris Denorfia hit a groundball single up the middle in the third, and Will Venable bunted his way on in the sixth. Otherwise, Gonzalez would have challenged a no-hitter. He pumped 94-mph fastballs at the knees, striking out six while letting only three balls escape the infield. With his 91st and final pitch, Gonzalez struck out Chase Headley swinging at a 93-mph fastball.

“I was just going out there trying to pound the strike zone, and not worry about what was going on after that,” Gonzalez said. “It’s definitely a credit to the catchers and my defense.”

Their first brutal reminder of life without Zimmerman came in the very first inning. Ian Desmond led off by reaching on an error, and Danny Espinosa walked. The Nationals had every ingredient for a rally, except walking to the plate in Zimmerman’s place was DeRosa, a 37-year-old veteran who was 3 for 30 on the season.

Not long before Zimmermann slid into the MRI tube, DeRosa hit an easy groundball to short, and Bartlett started a 6-4-3 double play. Werth then smoked a line drive to right field, but it found Venable’s glove, and the rallied died with a zero on the board.

The zeros kept piling up, even after Adam LaRoche led off the fifth with a double. They may not have much offense, and Zimmerman’s impending diagnosis only threatened to enhance that worry. But, with their rotation, the Nationals always have hope.