Davey Johnson angrily sprung out of the Washington Nationals’ dugout and loped toward the first base umpire as fast as his 69-year-old legs could carry him. Saturday afternoon had reached a critical moment. The Nationals led the Atlanta Braves by two runs on the field and, at the time, 71 / 2 games in the standings. The middle of the Braves’ order beckoned. The leadoff man had just reached base on what Johnson thought — what he was sure — was a bad call.

“Even with my old eyes,” Johnson said later, “I knew I was right.”

The Nationals’ manager would soon stomp back to the dugout, arms flailing, ejected for the first time this season and about to absorb the second of two moments that breathed a small measure of life into the race for the National League East. The Braves followed a blown call with Jason Heyward’s two-run, game-tying homer off Edwin Jackson, the turning point of the Nationals’ 5-4 loss at Turner Field.

The Braves sliced Washington’s lead to 61 / 2 games with one more showdown looming Sunday night. The Nationals still hold a commanding edge with 17 games to play. But they could have all but stamped out the Braves’ chances Saturday, if they had held a four-run lead and if not for an eighth-inning implosion by reliever Ryan Mattheus.

Mattheus faced five batters in the eighth inning, and he allowed a hit and two walks before he forced in the winning run with a fastball that grazed Andrelton Simmons’s jersey. But the game swung long before Mattheus even entered, on a call that could linger if the Nationals do not secure a few wins in the near future.

“Winning this series makes [the Braves winning the East] more realistic,” Heyward said. “Our mind-set is to go after the division until you can’t.”

The Nationals took a four-run lead into the bottom of the second inning, paced by Adam LaRoche’s 30th homer and sloppy defense from the Braves. Jackson cruised along despite a few rough patches, and after five the Nationals led by two.

Leading off the sixth inning, Martin Prado ripped a one-hopper up the middle. Jackson knocked it down with his glove, scampered to his right and fired to first base. LaRoche stretched, and the throw arrived in time. But first base umpire Marvin Hudson ruled LaRoche had come off the bag and called Prado safe. Replays showed LaRoche had stayed on. LaRoche did not need to see them.

“I was sure,” LaRoche said. “For whatever reason, he couldn’t tell. He couldn’t see it. It cost us a big run.”

Jackson immediately pointed at the base and screamed. Johnson came scuttling out of the dugout and screamed in Hudson’s face. Johnson demanded Hudson appeal the call with home plate umpire Marty Foster. Hudson refused. Johnson argued until Hudson threw him out. The Nationals manager swung his arm in return, as if to feign ejecting the umpire.

“If I can see it from 150 feet that the throw beats him, and he’s on the bag and he was out of position, I wanted him to get help,” Johnson said. “Those are critical points in games. I’ve got old eyes and I can see that. He’s a good umpire. I felt like the object is to just get this right. We don’t need to give them a little added momentum here. Get some help. I probably overreacted, but it was really a critical point in the ballgame. My pitcher pitched a heck of a ballgame. We had a lead. We don’t need to give them any gifts.”

Still enraged, Jackson pitched with no outs to Heyward. He fell behind, 2-0, then got back in the count with a slider. Jackson then threw a fastball down the chute, and Heyward clobbered it. The stadium erupted as the ball soared over right-center field fence, tying the score at 4.

“At the end of the day, he called him safe,” Jackson said. “Once he makes the call, at that point, it really doesn’t matter. He’s still on first base. The game has to continue.”

Jackson would face one more batter, striking out David Ross, before bench coach Randy Knorr, subbing for Johnson, came to take the ball. After 86 pitches, 57 of them strikes, he was done with no chance to win. Jackson watched the remainder of the inning alone at the end of the bench, resting his arms on the railing.

“My job is to go out there and secure the lead, regardless of the calls being made,” Jackson said. “I can’t really control that. I have a job to go and get outs.”

Knorr tabbed Mattheus for the eighth. In the bullpen, Mattheus fired strikes and felt confident in his stuff. He had walked more than one batter in only three of his 58 appearances this season, and had hit just two batters. In a span of five batters, he walked two and then hit a batter.

“That’s inexcusable,” Mattheus said. “I didn’t even give us a chance to win that game. I’ve got to throw strikes. If I get beat throwing strikes, it’s a little easier to swallow. I can’t remember that happening any time in the past. It’s inexcusable.”

Zach Duke squirmed out of a bases loaded, one-out jam to keep the score at 5-4. With Braves closer Craig Kimbrel warming up, on most nights the lead may well have been 10. Friday night, Kimbrel struck out three Nationals with 10 pitches.

Saturday, Washington put a scare into him. Chad Tracy lined a pinch-hit single to left field with one out, and pinch-runner Eury Perez stole second and sprinted to third on an errant throw.

They still had to get a hit. Kimbrel struck out Steve Lombardozzi. Then he ended the game by striking out Tyler Moore swinging through a 97-mph fastball. Kimbrel had struck out the side again.

The crowd erupted. The Nationals retreated to their clubhouse, upset at the crucial call but also at themselves. “We could’ve done a better job getting guys on base,” LaRoche said. They will turn Sunday to Cy Young candidate Gio Gonzalez to salvage one win, and to put a frustrating day behind them.

“It’s like crying over spilled milk,” Johnson said. “It’s over.”