Henry Rodriguez (Jonathan Newton/The Washington Post)

The Nationals, who have begun the season with two disappointing months and a 28-29 record, made sweeping changes to their roster on Tuesday afternoon and overhauled their bullpen, adding top prospect Anthony Rendon, welcoming right fielder Jayson Werth back from the disabled list, shipping out two relievers and placing scuffling second baseman Danny Espinosa on the disabled list.

The Nationals designated left-hander Zach Duke and right-hander Henry Rodriguez for assignment. They called up Ian Krol, a 22-year-old lefty acquired in the Michael Morse trade, from AA Harrisburg. In one day, the Nationals made three moves involving six players, their largest day of transactions this season. Seven of the 25 players on the Nationals active roster, over a quarter, weren’t on the roster on opening day.

“It wasn’t for the jolt scenario,” General Manager Mike Rizzo said. “More like getting guys here that give us the best chance to win baseball games. … It’s about putting the best 25 out there at this particular time to help win games. Decisions would be different if we had a full healthy team the whole season and we were hitting on all cylinders. But we’re not healthy and trying to piece together a lineup to help us scratch together enough runs to win some games. We felt like to get healthy players to give us a chance to be as good offensively as we can.”

Espinosa landed on the disabled list for his fractured right wrist, which was hit by a pitch on April 14. The fracture (and bone chip) wasn’t discovered until May 24. Espinosa, who was already playing with a rehabbed torn rotator cuff in his left shoulder, was among the least productive hitters in baseball, hitting .158/.193/.272 and his performance, although stellar in the field, showed he was compromised at the plate.

Espinosa is expected to see a hand specialist on Friday, and receive MRIs on both his wrist and shoulder. The Nationals want him healthy and a stint in the minors to fix his hitting mechanics is possible.

The Nationals now turn to Steve Lombardozzi and Anthony Rendon to man second base. Rendon, the organization’s top hitting prospect, was just recently promoted to Class AAA Syracuse on Friday with the specific mission to play second base. He played only three games with Syracuse before receiving a surprising call-up on Tuesday morning. He has played only eight games at second as a professional.

Duke, 30, a former starter, struggled as the bullpen’s left-handed long man and posted a 8.71 ERA in 20 2/3 innings. The Nationals signed him to a one-year, $700,000 deal this winter after he resurrected his career with them in Syracuse last season. Rodriguez, 26, the fire-balling right-hander the Nationals acquired in a 2010 trade with Corey Brown for Josh Willingham, confounded the Nationals for the better part of three seasons with overwhelming stuff but head-scratching wildness that caused him to post a 4.00 ERA and walk 16 batters in 18 innings.

With right-hander Erik Davis in the fold since his call-up on Saturday, the Nationals called up Krol from Harrisburg, where he posted a 0.69 ERA in 26 innings with a 4.14 strikeout to walk ratio.