Ryan Zimmerman broke his right thumb as he slid into second base when he was picked off in the fifth inning of the Nationals’ loss to the Braves. (Mike Zarrilli/Getty Images)

This Washington Nationals season, nearly two weeks old, has been marked by two exasperating themes: a growing list of injuries and frustrating losses to the Atlanta Braves. While enduring another defeat at the hands of their NL East rivals Saturday, the Nationals suffered a far more damaging blow: Third baseman Ryan Zimmerman, one of the team’s cornerstones, fractured his right thumb and will miss four to six weeks.

Zimmerman, 29, jammed the finger as he dived back to second base on a pickoff in the fifth inning of a messy 6-3 loss to the Braves, the Nationals’ fourth loss in five games to Atlanta.

The blow came only a few hours after center fielder Denard Span was placed on the seven-day disabled list with a concussion and Jayson Werth was held out of the starting lineup with minor groin tightness. The Nationals are already without their primary catcher, Wilson Ramos (fractured bone in his hand); their prized offseason acquisition, starter Doug Fister (lat strain); and backup outfielder Scott Hairston (oblique).

But losing Zimmerman — a team leader, the longest tenured National and a crucial bat in the heart of the lineup — is a major blow.

“It’s a big one,” Manager Matt Williams said. “We don’t have a choice: Gotta go play and compete and win games.”

The Nationals fell to the Braves on Saturday because of the struggles of starter Taylor Jordan, defensive miscues and an offense that couldn’t deliver a big hit. The Nationals committed three errors, lost close calls and stranded 11 base runners. Jordan gave up four runs in the first and labored to get through five innings.

For all their talent and expectations, the Nationals cannot solve their division foe. Dating from the beginning of the 2013 season, the Nationals are 7-17 against the Braves. If the Nationals want to win a second division title, they need to figure out how to beat this team. But keeping their team intact may be a more pressing concern.

The Nationals’ opening day lineup lasted seven innings before Ramos left the game with a fractured hamate bone. Since then, the Nationals have endured a bizarre first two weeks under first-year manager Williams.

“It’s pretty bad, pretty bad luck on our part,” said Anthony Rendon, who led off the game with a home run. “But that’s part of the game, and you’ve got to pull together as a team and pull through.”

Adding insult to Zimmerman’s injury was that he was out on the pickoff play, helping squash a two-on, one-out rally in the fifth. Shortstop Andrelton Simmons came behind Zimmerman and tagged him as his right hand reached out to the base. After he was called out, Zimmerman sat on his knees and looked at his right thumb. He got up slowly, his right arm hanging by his side and his finger bloody. Fans were unhappy he took so long to head toward the dugout, booing some as he walked off the field.

Zimmerman was met by a trainer in the dugout and replaced in the bottom half of the inning by Rendon at third, with Danny Espinosa taking over at second. Rendon will take over third base during Zimmerman’s absence, with help from utility man Kevin Frandsen.

“It’s not our first choice certainly, but the fact that they can play multiple positions is good in times like this,” Williams said. “Certainly never want to miss someone like Zim for that amount of time, but it is what it is. There’s nothing we can do about it now but play.”

Williams wouldn’t say who would be called up from the minor leagues, but Class AAA Syracuse infielder Zach Walters was pulled in the fifth inning of the second game of a double header Saturday, presumably to head to Atlanta. Walters had an impressive spring at the plate and is hitting .310 with an .805 OPS through eight games at Syracuse.

Zimmerman was hitting .364 with two home runs and six RBI. This is the fourth straight April that Zimmerman has landed on the disabled list. He is in the first year of the six-year, $100 million extension he signed two years ago.

The Nationals already began the game without three of their regulars. Because of the injuries, the Nationals used an outfield alignment of Bryce Harper in center, Nate McLouth in right and hot-hitting Frandsen, primarily an infielder, in left field. Werth pinch-hit in the eighth inning Saturday and singled, and afterward he said he felt better. He could be available to return to the lineup Sunday.

“When you get the four of them back, with Denard, Willy, Doug and Z, it’s a pretty good trade deadline in May,” Frandsen said. “It’s not the end of the world. It’s April. It [stinks], but at the same time no one is going to feel sorry for you.”

Jordan’s struggles notwithstanding, the Nationals’ offense was the major culprit for Saturday’s demise, going 1 for 16 with runners in scoring position. In the fourth inning, Harper walked and Frandsen singled, but catcher Sandy Leon flied out and Jordan failed to lay down a bunt, which got Harper caught in a rundown. Zimmerman’s pickoff and an Adam LaRoche strikeout killed a potential rally in the fifth. Rendon flew out with runners on the corners with two outs in the eighth.

After the game, the Nationals walked off the field here after another defeat to their division foe not only worrying about their struggles against the Braves but also about their wounds.

“It’s tough,” McLouth said. “Those kinds of things happened unfortunately, and it’s been a barrage here in the first two weeks of the season. You can’t complain. I’m sure the Braves don’t want to hear anybody complain of any injuries because they’ve had some, too. You have to overcome.”

More on the Nationals:

Nationals Insider: Treinen called up to give bullpen fresh arm

Nationals Insider: Werth’s groin improving

Nationals Insider: Clippard’s struggles vs. Braves continue