Now they'll meet in an important three-game series beginning Tuesday night.
The situation isn't nearly as dire for the Phillies, who find themselves tied with Braves, but the Nationals are 7 1/2 games back and may have used up all of their mulligans.
Washington (62-63) dropped two of three games to the Miami Marlins, who are in last place in the National League East, and have lost six of eight.
Philadelphia (68-56) hasn't floundered quite as badly, winning five of their last 13, but dropped three of five games to the New York Mets while the Braves were losing four straight to the Rockies.
"We understand that we've had some missed opportunities to take some steps forward here," Phillies manager Gabe Kapler told MLB.com after the Phillies lost 8-2 Sunday in the Little League Classic in Williamsport, Pa.
"So, at this very moment, I'm not thinking about how fortunate we are. I do feel like we're in a good spot in the standings, but I'm thinking about the fact that we need to take the day off, regroup and get ready to play the Nationals."
The Nationals have some regrouping to do themselves. After losing in extra innings Saturday night, they were manhandled by the Marlins 12-1 on Sunday, getting just two hits off starter Jose Urena, who tossed his first career complete game.
Washington starter Gio Gonzalez (7-10) continues to struggle, allowing eight runs and 10 hits in 4 2/3 innings.
"I think it was in all honesty an ugly game. And everybody saw it," Nationals manager Dave Martinez said.
Before Sunday's game, Martinez announced that right-hander Stephen Strasburg (cervical nerve impingement) will come off the disabled list to pitch the second game of the series Wednesday night. He'll be sandwiched between Tanner Roark and Max Scherzer.
"It's nice to be able to go into that series with our three best pitchers," Martinez said.
Added outfielder Adam Eaton to MASN.com: "A good week or two, a sweep of two teams that are ahead of us, can get us right back in the ballgame. But we've got to do it now."
Roark (8-12, 4.13 ERA) struggled in the first half, but the right-hander is 5-0 with a 1.77 ERA overall since the All-Star break. Last time out, Roark picked up a win when he allowed four runs (three earned) in six innings against the St. Louis Cardinals.
He is 0-3 with a 5.40 ERA against the Phillies this season and 6-9 with a 4.18 ERA in 20 games (18 starts) in his career.
Right-hander Vince Velasquez (8-9, 4.13) gets the opener for the Phillies. He has allowed seven runs and 10 hits in 6 1/3 innings in his last two starts.
Velasuez got the win when he faced Roark and the Nationals on May 5 and took a no-decision against Washington on June 30. He's 2-2 with a 5.28 ERA in six starts against the Nationals.
Tuesday will tell who was better able to bounce back from a disappointing weekend.
"There's still quite a bit of baseball left," the Phillies Nick Pivetta, Sunday's losing pitcher, told MLB.com. "There's not a ton, but there's still a good enough amount where nights like these you can brush them off your shoulders and take the off-day tomorrow, regain your strength, go into Washington.
"I know these men in here. (Tuesday) we're going to go in there, we're going to look for the sweep against those Nationals."