Left fielder Kevin Frandsen throws the ball against the Miami Marlins at Nationals Park on Sept. 26, 2014. (Ricky Carioti/The Washington Post)

The Washington Nationals claimed their second National League East Division title in three years this season, won a league-leading 96 games and are one of the most popular picks to win the World Series. They somehow reached this point after having all eight regular position players active at the same time for just 27 of 162 regular season games. How did a team whose key players missed a combined 365 games on the disabled list claim the NL’s top seed?

The answer is a combination of depth and shrewd roster moves mixed with creativity and perseverance.

“It’s easily forgotten that we were without key players for a long time and three of them at the same time for a long time,” General Manager Mike Rizzo said. “Other teams have folded. We grinded through it. It’s a testament to Matt Williams and those bench players who filled in when we were at our weakest. It’s the depth of the organization. The Blake Treinens giving us spot starts and quality innings. It’s the Kevin Frandsens in the outfield when he rarely played there before. There’s enough credit to go around. This thing doesn’t happen if you don’t go 35, 45 [players] deep.”

The Nationals will host the San Francisco Giants, the winner of Wednesday night’s NL wild-card game, because they withstood injuries to Doug Fister, Gio Gonzalez, Bryce Harper, Adam LaRoche, Wilson Ramos, Denard Span and Ryan Zimmerman.

Rizzo “and the guys in the front office know that in order to win in this league you have to have a lot of depth,” Zimmerman said. “Our minor league system has unbelievable players. The guys they signed here to be bench guys that fill in when everyday guys get hurt have a done a great job. Those guys are just as important to this team as any one of us.”

Despite a slow start to the season and injuries to Ryan Zimmerman and Bryce Harper, the Nationals have few glaring concerns heading into the playoffs. The Post Sports Live crew discusses what could hold the Nationals back from a deep postseason run. (Post Sports Live/The Washington Post)

During a disappointing 2013 season, the edges of the Nationals’ roster failed them. The bench struggled, and the bullpen wasn’t properly constructed.

This offseason, the front office was more aggressive in addressing both areas — signing Frandsen when he was cut by the Phillies, trading for Jerry Blevins — and benefited from the development of young players such as Aaron Barrett, Tanner Roark and Treinen.

The Nationals also added depth. By trading for Doug Fister in the offseason, the Nationals could move Ross Detwiler to the bullpen and allow Roark to thrive as a starter. Sending pitching prospect Nate Karns to the Tampa Bay Rays in a spring training trade yielded veteran catcher Jose Lobaton. That move proved critical when Ramos went out with hand and hamstring injuries. Although Nate McLouth hit .173 this season and landed on the disabled list himself with a shoulder injury, signing him in the offseason to a two-year, $10.75 million deal gave them insurance against injuries to Harper, Span and Jayson Werth.

“We survived by the depth we built,” Rizzo said. “We worked hard on the bench in the offseason.”

And the rest of the roster pulled its weight. Bounce-back seasons from LaRoche and Span, the everyday play of Ian Desmond, strong hitting by Werth and the breakout season by Anthony Rendon carried the Nationals during injuries. A strong April at the plate by Danny Espinosa and Rendon’s ability to play both third and second, a skill he added last season, also helped fill holes. At one point in early May, LaRoche, Fister, Zimmerman and Harper were on the disabled list together. Filling out a lineup wasn’t easy.

“I heard someone say the other day that at one point we were 27-28 and how bleak it was,” Williams said. “It wasn’t that bleak. It wasn’t that bad. We understand that we have injuries and have to get these guys back, but let’s just kind of tread here. We’ll try and be competitive every day and win the ones we can and at some point we’ll get everybody back.”

During LaRoche’s brief absence, Frandsen manned first base with some help from Tyler Moore and Greg Dobbs. But his biggest contribution may have been in left field. He entered the season with just three starts there but was forced into outfield action when Harper injured his thumb. In all, the 32-year-old veteran utility man started 15 games in left field, platooning the position with McLouth and Scott Hairston. Frandsen appeared in 105 games, playing first, second, third and left field, and hit .259 . His versatility outweighed his offensive output.

The Post Sports Live crew debates whether the Nationals will be disappointed with anything less than a World Series title after the end of an incredible regular season. (Post Sports Live/The Washington Post)

“We didn’t know Harp was going to be gone that long,” Rizzo said. “In that regard, we didn’t expect [Frandsen] to play left field hardly at all [when we signed him] because Harp was going to be out there for us. Once he got hurt, I knew he was a viable option and could handle the position and know he brings a solid at-bat every time up.”

When injuries depleted the lineup, the biggest strength of the Nationals’ system was at its best. The pitching staff carried the team, leading the majors with a 3.03 ERA this season thanks to strong seasons from Drew Storen, Tyler Clippard, Jordan Zimmermann, Stephen Strasburg, Roark and Fister.

“That was a constant, with the exception of Doug out to start the year,” Williams said.

After Taylor Jordan struggled filling in for Fister in April, the Nationals needed one spot start before Fister returned. So they turned to 26-year-old Treinen, a seemingly small piece of the 2012 Michael Morse trade. The hard-throwing sinkerballer impressed in big league spring training as a reliever and broke into the big leagues in mid-April as a reliever when the Nationals needed bullpen help. When Treinen went back down to Class AAA Syracuse, the Nationals outlined their plan to stretch him out into a starter.

“The innings in spring training helped,” Treinen said. “An inning here and there. The bullpen prepared me for starting, and the starting prepared me for the back and forth, which was nice. It was fun to get the opportunities.”

Treinen made a solid spot start May 6, then returned later in the month to fill in for Gonzalez for nearly a month. In 36 innings spread over seven starts, Treinen posted a 3.00 ERA, and the Nationals view him as a piece of their future as a starter.

When players were sent down to Syracuse, the Nationals conveyed a clear message to each of them on how they could improve and come back to help. When a tiring Barrett, 26, was sent down in late July, pitching coach Steve McCatty and Williams explained to him that they wanted him to work on his change-up, to rest and be ready for September.

“The big thing for me was having a plan in place and communicating that with the player,” said Syracuse Manager Billy Gardner Jr., who talks regularly with Williams, Rizzo and assistant general manager Doug Harris. “The player needs to know what to work on and he can go out and do it.”

Rizzo also adjusted on the fly. After Zimmerman severely strained a hamstring in late July, he traded prospect Zach Walters to Cleveland for veteran rental player Asdrubal Cabrera. With Cabrera, the Nationals went 35-14. When the bullpen began to wear, Rizzo grabbed veteran left-hander Matt Thornton off waivers.

Players also adjusted. Before Zimmerman returned from his broken thumb in early June, the Nationals approached him with the idea of learning to play left field to help fill the offensive void left by Harper. Zimmerman, whose balky right shoulder was affecting his throwing at third, put the team first and agreed.

“The idea came from necessity,” Rizzo said. “It’s the mother of invention. The way we were playing without Bryce and Zim in the lineup, when Zim came back, we felt we needed to keep Rendon’s bat in the lineup and we needed to be better defensively with Espinosa at second. How are we going to do this when Zim comes back? I knew Zim was athletic enough to play several positions.”

Because injuries forced rookies into major roles and other players into less familiar ones, the now-full-strength Nationals are in an enviable position. When Rafael Soriano struggled in the second half, the Nationals turned to former closer Storen in the ninth inning. Roark may not even crack the postseason rotation. Zimmerman may be an option off the bench or play any of his three positions. Barrett has been strong since his return. The Nationals are deep and streaking into the playoffs.