Nationals pitching coach Steve McCatty argues with home plate umpire Corey Blaser during the third inning. McCatty was ejected. (Thearon W. Henderson/Getty Images)

Gio Gonzalez handed the baseball to Washington Nationals Manager Matt Williams without hesitation, walked off the mound Saturday night as the San Francisco Giants fans at AT&T Park roared, and made a beeline for the dugout. His teammates, sitting on the bench or hanging on the railing, stared blankly out at the field. There wasn’t much to say.

The Nationals fell, 12-6, for their fifth straight loss on this potentially-season-defining West Coast trip and reached a new low point in their second-half slide, falling to .500 on the season. They are 10-19 since the all-star break and 58-58 overall. Adding to the misery: their best player, Bryce Harper, left the game in the seventh inning with a minor injury after fouling a ball off his left foot.

If the Nationals are going to snap the skid Sunday, they will have to do so against Giants ace Madison Bumgarner. The only small piece of salvation for the Nationals on Saturday came in New York, where the Mets lost to the Pirates, 5-3, in 14 innings to keep Washington’s deficit in the National League East at 4 1/2 games.

“It’s a loss,” Manager Matt Williams said. “We have a lot to play. Rock bottom? We’re still in this hunt. So no. We’ve got to play better.”

The Nationals could still make a run, but that would require finding the bottom of this skid. It has yet to come. Forty-six games remain. The strong NL Central teams such as the Pittsburgh Pirates and Chicago Cubs are firmly in command of the two wild-card spots. The Nationals are further out of the second wild-card spot (9 1/2 games) than their own division.

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“We believe,” shortstop Ian Desmond said. “We’re still together. We’re united. We’re pulling for each other. I believe that as long as we pull for each other and we still believe we’re in good shape. We’re four-and-a-half games back with a lot of games left to play. It’s not easy but we’ve still got each others’ back and we still believe in each other and we’re fighting for each other.”

At their current rate, the Mets are on pace to win 87 games. In order to also reach that mark, the Nationals must go 29-17 the rest of the way. The Mets have the dominant starting pitching that prevents long losing streaks. The Nationals, on talent alone, have the same type of rotation but simply haven’t performed.

The two times the Nationals won their division, in 2012 and 2014, they pulled away in the final third of the season. This year they are sputtering, none of the facets of their team performing in sync.

Gonzalez entered with a 1.48 ERA over his previous eight starts, the Nationals’ top starter over that span. But true to his team’s current state, his left arm wasn’t enough.

“I took the momentum out of our hands,” Gonzalez said. “Falling behind on everyone. It doesn’t help, especially when we needed a big bounce-back.”

Gonzalez made it through the first two innings without issue, staked to a 2-0 lead thanks, in part, by Desmond’s mammoth 477-foot home run off Giants starter Jake Peavy, the longest by any National this season.

Then Gonzalez’s command undermined him. He left balls up and missed his spots, and the Giants hammered the pitches. Six straight Giants reached base to start the third: triple, walk, walk, RBI single, three-run double, RBI single.

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“It’s pretty rough right there,” Harper said. “Going into a game we felt like we could win. Started off pretty well.”

After the second walk loaded the bases, pitching coach Steve McCatty came out to chat with Gonzalez. As McCatty walked back toward the dugout, something was said between him and home plate umpire Cory Blaser. McCatty and Blaser then stood face to face in animated conversation. McCatty, normally even-keeled during games, was ejected for the first time in his major league coaching career.

“I don’t know what happened,” Gonzalez said. “I don’t even know if Cat knows what happened.”

Gonzalez eventually gave up one more run, putting the Nationals in 6-2 hole before he was replaced with Tanner Roark. Over the next 2 1/3 innings, Roark gave up three runs.

The Nationals injected some intrigue into the game in the sixth inning with a three-run rally. With a big deficit, it only made a small dent. Jose Lobaton’s double drove in two runs, and Michael Taylor’s triple trimmed the Nationals’ deficit to 9-5. But Nationals reliever Felipe Rivero gave the Giants more cushion, as did Drew Storen in mop-up duty.

Harper’s injury was the final gut punch of the night, although it turned out to be minor. Facing Giants reliever George Kontos, Harper fouled a ball off the top of his left foot. Harper instantly jumped back in pain and hobbled around. After a quick visit by the Nationals’ assistant trainer, Harper finished the at-bat and lined out. He was replaced in right field in the bottom of the inning by Jayson Werth.

Harper said the ball hit a nerve in his leg and felt “very, very painful.” He said X-rays were negative and he would wait to see how he felt before Sunday’s game. The Nationals will need him if they want to stop this slow bleed.

“It’s about coming in here and keep having fun and enjoying the game,” he said. “It’s hard to do definitely but we play a game for a living. There are a lot of things that are bigger than life and this game just got to take it one game at a time and keep enjoying it and doing what we’re doing and hopefully we’ll come in here one day and it’ll turn.”