It’s all come apart for Dan Uggla and the Atlanta Braves in recent weeks as the Nationals swept by them into first place in the NL East and the Phillies swept them in a three-game series this week. (Curtis Compton/AP)

When the Washington Nationals and Atlanta Braves met in April the outlook for both teams could not have been more different. The Braves were in the midst of another hot start, much like they did last season en route to winning the National League East title, and the Nationals continued their puzzling struggles against them. The Braves swept the Nationals out of Atlanta — outscoring them, 23-11 — and the already hobbled Nationals lost Ryan Zimmerman and Denard Span to injuries.

More than two months later, the rivals face off in a four-game series beginning Thursday at Nationals Park. The wobbling Braves, losers of eight of their past 12 games, couldn’t take advantage of Washington’s slow start and Tuesday night, the Nationals took over the lead in the NL East. Atlanta’s starting rotation has swapped in new parts and been the team’s strength, but its usually dominant bullpen has looked vulnerable and its offense erratic.

“We haven’t played great,” Braves shortstop Andrelton Simmons said. “Our pitching has kept us in a lot of games. Our offense has showed signs of what it’s capable of doing but we need to be more consistent.”

Added third baseman Chris Johnson: “We’re just trying to find ourselves, really.”

The Nationals are healthier — getting back Zimmerman and Span as well as Doug Fister — and have won 12 of their past 18 games. Since starting 17-9, including winning five of six against the Nationals, the Braves are 19-26.

“I’m hoping our best baseball is ahead of us,” Braves General Manager Frank Wren said. “We played fairly well early out of the gate and, like everyone else, we’ve had some inconsistencies that we’re trying to tighten up.”

The Braves suffered major injuries to their rotation, yet their starters’ 3.24 ERA ranks in the top five in the majors. Kris Medlen and Brandon Beachy had Tommy John surgery in March. In the first month of the season, with a rotation of Julio Teheran, Ervin Santana, Aaron Harang, Alex Wood and David Hale, the Braves had a major league-best 2.32 ERA. Santana, signed in mid-March for one year at $14 million as a stopgap for injuries, debuted on April 9. After two injuries, Mike Minor joined the rotation on May 2. Gavin Floyd, an Annapolis native signed in the offseason, made his first start back from Tommy John surgery on May 6.

But with each passing month, the rotation’s performance has slipped. In May, it had a 3.48 ERA. So far this month, it is 4.85. Minor (4.42) and Santana (4.12) have struggled of late, while Floyd (2.98 ERA) has been good. The Braves have thrived thanks to their depth, dominant pitching from Teheran (2.31 ERA) and strong performances from Harang (3.83 ERA).

“They’ve done a terrific job,” Wren said. “It’s allowed us to get to this point.”

The bullpen, however, has been shaky. Its 3.55 ERA is 13th in the majors; a year ago it was the lowest. Hard-throwing setup man Jordan Walden missed most of May and flame-throwing setup man David Carpenter landed on the disabled list on Tuesday.

“When [Walden] was on the DL it seemed like we were having trouble getting it configured and getting the performance that we were looking for leading up to [closer Craig] Kimbrel and that cost us some ballgames,” Wren said.

The Braves’ up-and-down offense has also been a weakness. Last week in Colorado, for example, they scored 13 runs in one game and were no-hit through five innings by a rookie making his major league debut in another. Only one team, the San Diego Padres, scores fewer runs than the Braves’ 3.63 a game. They don’t get on base often (fifth-worst .306 on-base percentage), strike out a lot (fourth-most with 616) but hit a fair amount of home runs (10th, with 70).

The Braves finally benched struggling second baseman Dan Uggla and his .164 average in favor of hot-hitting prospect Tommy La Stella (.348). Despite a .209 average, B.J. Upton is playing every day in center field. Justin Upton, Evan Gattis and Freddie Freeman have carried the offense.

“It’s easy to win when you have a big inning,” Justin Upton said. “We’ve got to do a better job of chipping away and scratch that run across even if it doesn’t tie the game or tacking on the extra run. Sometimes you can depend on the big inning and we’ve done that a little bit too much.”

What most frustrates many Braves is the inability to take advantage of the Nationals’ struggles in May; Washington was 11-15 but Atlanta was only slightly better (13-16).

“The opportunity was there for us to pull away, obviously, with the Nationals going through all the injuries they’ve had,” catcher Gerald Laird said. “And now they’re starting to get healthy and starting to get in the mix. Not to say anything bad about that baseball team — they’re a great baseball team — but we beat them last year when they were at full strength and we were at full strength. We know we can beat them. They can beat us, but we know we can beat them if they’re either full strength or with some injuries.”

The Nationals’ struggles against the Braves have confounded not only people in Washington but in Atlanta. Braves officials and players don’t know why they have hammered the Nationals, a talented and familiar opponent, so often in recent history. The Braves are 18-7 against the Nationals since 2013, outscoring them 73-49, posting a team 2.21 ERA and playing stronger defense.

The Braves have “come out on the winning side of it more than we’d like,” General Mike Rizzo said after two tough losses in April. “But we feel confident against this team. We feel we’re better than this team. We respect them, and we respect their organization. But we don’t fear them. We think we’re the better team, and at the end of the day we’re going to come out on top.”

The Braves certainly noticed Rizzo’s statements, but they don’t appear to be bothered by them.

“He’s right,” Johnson said. “I don’t think they’re afraid of us at all. I know some of their guys over there and I’m sure they’re ready to play us now because they’re playing some good ball. They’ve got some guys that were hurt when they came over there the first time. Next time we face them we’re going to get their best ball. We’re not afraid of them, they’re not afraid of us. It’s one of the great rivalries in baseball.”