ST. PETERSBURG -- As Matt Duffy entered the offseason, he knew that he needed to add strength in order to hold up over the course of a 162-game season.

After missing all of 2017 with a left Achilles injury, Duffy was set to replace longtime face of the franchise Evan Longoria as the Rays' everyday third baseman in '18. In the first half of the season, Duffy didn't disappoint -- he was one of the best hitters in the Tampa Bay lineup. After 80 games, Duffy had a .317/.371/.413 line, and it looked like he was finally over the Achilles injury that had plagued him starting in '16.

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The second half of the season, however, was a different story. Duffy's production steadily declined and he began to get more days off in order to try and keep his body fresh. While the Rays and Duffy tried different things, it was apparent that his body just wasn't holding up over the course of the year. Over the last 52 games, Duffy's line dipped to .257/.347/.288, and he connected on just six extra-base hits in the second half.

"I completely hit a wall," Duffy said. "I didn't hit for much power at all. I think I hit a couple of doubles, that was it. I wanna be able to play more than three or four games without having [manager Kevin Cash] coming in and telling me that my legs are going to fall apart. That was the biggest motivation."

Because of those struggles, Duffy mapped out a plan to gain strength during the offseason. As soon as the season ended, Duffy went straight to Phoenix, Ariz., looking to add about 10 pounds. His goal was to reach 180 pounds, but he surpassed that and is now at 189 pounds heading into Spring Training. He hopes the added strength will help him turn some singles into extra-base hits in 2019.

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"It's the heaviest I've ever been," Duffy said at Saturday's Fan Fest. "I feel good, at least in the workouts and stuff, so we'll see how it translates to the field."

Duffy spent most of his time at Exos, which is a physical fitness program in Arizona, where he worked on strength, speed and agility. The facility also provided him with a meal plan, which helped him eat enough in order to gain the desired weight.

"The first couple of weeks were tough. I pretty much felt like I was going to throw up all day, but after that, my body adjusted and it was pretty smooth sailing from there," Duffy said.

The 28-year old has been at the Rays' Spring Training facility in Port Charlotte, Fla., for about a week, and he believes his improved shape will help the team fight for a playoff spot in 2019. Duffy played exclusively at third base last season, but he has made it clear that he's willing to play anywhere, as long as it gets him in the lineup. It's possible that Duffy will get some reps in the outfield during Spring Training as the Rays try to find at-bats for what appears to be a crowded infield, with Daniel Robertson , Joey Wendle and Brandon Lowe all in the mix.

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Now that Duffy has reached his offseason goal, it's time to display it on the field. He said that he's been ready to go for weeks, and a lot of that has to do with the potential Tampa Bay has heading into the year.

"We truly believe that we can beat anybody and we can compete with anybody," Duffy said. "Now, we can't get too far ahead and start thinking that we're going to win 100 games every day, because that's not how you win 100 games. We have to stay focused on the little things that we can control."

Juan Toribio covers the Rays for MLB.com. Follow him on Twitter @juanctoribio.