To Boston Red Sox manager John Farrell, it hardly seems possible that just 11 months ago his team was celebrating the World Series championship on the field at Fenway Park.

Since then, the ballclub has plummeted to the bottom of the AL East standings, completing a roller-coaster ride from worst to first and back to the division cellar that is unprecedented in baseball history.

“It’s hard,” general manager Ben Cherington said on Monday, a day after the Red Sox wrapped up the season with a 71-91 record and fifth-place finish. “Obviously, you like the upside. But the downside is hard to deal with and painful for everyone involved. It’s not what we want to be.”

A year after going from last to the franchise’s third World Series title in a decade, the Red Sox are again looking to rebuild a depleted roster. Cherington said the priorities this offseason will be to add to the rotation that was dismantled at midseason  — four of the five starters were dealt before the trade deadline — along with a left-handed hitter and help for the bullpen.

The Red Sox also hope to have healthier versions of David Ortiz, Dustin Pedroia, Mike Napoli and Shane Victorino — all key parts of the 2013 championship team. They are also hoping midseason acquisition Allen Craig will bounce back, having never found his form after the trade from St. Louis.

Plus, there’s a lot of potential in Cuban outfielder Rusney Castillo, who made his made his major league debut two weeks ago.

If there’s one good thing about the team’s collapse, it’s that the front office has a head start on the offseason. Not just at the trading deadline, when Cherington was able to start building for 2015, but in the scouting and preparing for the free agent market.

“Plenty of work already happened,” he said. “But there will be plenty of work this month, too.”

Among the pickups at midseason was Yoenis Cespedes, who was acquired in the deal that sent Jon Lester to the Oakland Athletics. Cherington sought out hitters in the deals, he said, because he thought it would be easier to acquire them at midseason than as free agents.

But that leaves the team with an unproven rotation. Cherington traded Lester, John Lackey, Jake Peavy and Felix Doubront, and finished with Clay Buchholz, Anthony Ranaudo, Joe Kelly, Allen Webster and Steven Wright.

“They all did some good things and some not-so-good things,” Cherington said. “I think they’re all better for the experience.”

On other matters:

— Farrell said the team wants to have closer Koji Uehara back, even though he struggled in the role near the end of the season. He is a free agent.

— Catcher Christian Vazquez has the inside track at starting catcher, and David Ross has not been ruled out as a backup. If the team looks elsewhere for a No. 2 catcher, a lefty would be a plus but not a requirement.

— Young players such as Mookie Betts, Xander Bogaerts, Jackie Bradley Jr. will have a chance, but the team is concerned about depending too much on prospects.

Cherington said he knows they can’t win the World Series every year. But he expects to be competitive.

“Based on results from the last three years, we haven’t accomplished that yet,” he said. “But I believe we will.”

Also Monday, the Red Sox announced that they will keep the same average ticket price next year while expanding the variable pricing for high- and low-demand games. The 16 most coveted games will see increases by about $5 per ticket, with a corresponding decrease in prices for the low-demand games.

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