WASHINGTON -- Order another round for Atlanta Braves manager Fredi Gonzalez, who has learned that a winning streak can be tough to swallow.

The Braves won their 13th straight Wednesday night, summarily dismissing the Washington Nationals 6-3 to complete a three-game sweep and take a staggering-for-early-August 15½-game lead in the NL East.

Now Gonzalez will have to keep drinking up. It turns out that the streak happened to begin on the day that bullpen coach Eddie Perez first gave the manager some sort of protein drink. Gonzalez hates the taste, but he can't stop drinking it with his team on such a roll; sure enough, he was sipping the concoction from a cup in the dugout a couple of hours before Wednesday's game.

"They may be giving me poop. I don't even know what it is," Gonzalez said. "But I've been drinking them for 13 days in a row now. We're superstitious, you know."

Maybe there are some four-leafs clovers stashed in the clubhouse as well, the way the Braves have been playing. While they have a ways to go before they can mathematically clinch, this week has served as a psychological clincher that only could be undone by a monumental collapse.

"We came in here and we let 'em know," first baseman Freddie Freeman said. "We're here to stay."

Jason Heyward singled and Justin Upton doubled in a three-run eighth inning, Upton also homered, and Braves starter Kris Medlen (9-10) allowed three runs and three hits over seven innings. Craig Kimbrel pitched the ninth for his 36th save, working out of a bases loaded jam by getting Wilson Ramos to line out to right to end the game.

The eighth-inning runs came with two outs off relievers Ryan Mattheus (0-1) and Ian Krol as the Nationals lost their fourth straight and sixth of their last eight. The defending division champs scored only six runs in the three games and are losing hope for an alternate path to the postseason as well, falling nine games off the wild card pace.

"Lot of ground to make up, but you never know what can happen in this game," Nationals manager Davey Johnson said. "If nothing else, get our pride back by playing better."

The game was played nicely by both sides one night after a fastball to Bryce Harper's thigh cleared both benches and led to a public spat between the clubs' official Twitter feeds. Braves general manager Frank Wren said before the game that a tweet directed at Harper was "an inappropriate attempt at humor." When asked about any possible retaliation, Johnson said it would be "just baseball as usual" before flashing a smile.

As it turned out, the only confrontation involving Harper was between the young slugger and his own manager, when the two bickered in the dugout over whether Harper should come out of the game because of a nagging knee injury.

"Yeah, he was checking on my leg and asking how I felt," Harper said. "I just told him I felt fine and I don't want him to take me out."

While the game passed without incident between the two teams -- no one was hit by a pitch -- the saga might not be over. The teams play six more times this season, including a three-game series next week in Atlanta.

Meanwhile, Gonzalez has to stomach another protein shake. The good news: The Braves have Thursday off before opening a homestand.

"At least," Gonzalez said, "I get tomorrow off with the shakes."

Game notes

Andrelton Simmons started the rally in the eighth with a two-out double off Mattheus. After a walk to a pinch hitter, Heyward singled in a run off Krol. Upton followed with a two-run double to the left-field corner. ... Braves CF B.J. Upton has his first four-hit game of the season to raise his average to a season-high .198. ... Nationals RHP Tanner Roark made his major league debut with two scoreless innings. He also made a superb defensive play, diving to catch Medlen's sacrifice bunt attempt and throwing to first for a double play. ... Heyward returned to the lineup after leaving Tuesday's game with a strained neck muscle. "I felt a lot better when I woke up," he said. "Didn't have any head weirdness or headache or anything like that."