The Post Sports Live crew debates whether the Washington Nationals’ Ian Desmond or Danny Espinosa is struggling more after the first week of the season. (Post Sports Live)

The only thing that surprised Adam Dunn about the Washington Nationals’ success is that it happened so fast. The franchise was one of baseball’s worst when Dunn played here, but management’s plan changed things quickly — and left Dunn impressed.

Dunn’s former club has everything needed to win for a long time, which the Chicago White Sox designated hitter and first baseman believed even before the teams began an interleague series Tuesday at Nationals Park. With so much chatter about the Nationals in baseball, Dunn couldn’t help but hear some of it despite playing in the other league. The up-close Nationals experience actually is better than the hype.

So what’s the view from the visitors’ dugout at Nationals Park? Hard throwers in the rotation and bullpen, power hitters and smooth fielders throughout the lineup, a great mix of veterans and pups on the roster — what’s not to like?

“It’s really easy to say now because everything’s coming together, but you kind of knew it would,” said Dunn, playing in the District for the first time since leaving the Nationals as a free agent after the 2010 season.

“Am I saying I knew they would do everything they did last year? No. But even back when I was here, there were [signs]. You saw they were about to be really good in the future. You just didn’t know if it was going to be the near future or the very near future. It turned out to be the very, very, very near future.”

The Post Sports Live crew discuss the first two series for the Washington Nationals. After easily sweeping the Miami Marlins at home, the Nationals struggled against the Cincinnati Reds. (Post Sports Live)

Dunn’s unique assessment of time aside, you get the idea.

During the second of Dunn’s two seasons with the Nationals, they were a 93-loss mess. Just two seasons later, they emerged as a 98-victory force that won the National League East.

Starter Stephen Strasburg joined the rotation in Dunn’s final season with the Nationals. Also, the club drafted Bryce Harper that year, “and with those guys, you could see the beginning. They were making moves.”

Parting with Dunn was one of them. Dunn is a free-swinging slugger. When he connects, balls often wind up in the stands. When Dunn misses, baseball’s career strikeout records have to be updated. For two years, the Nationals lived with Dunn’s good (76 home runs and 208 RBI) and bad (376 strikeouts).

Then there was Dunn’s defense at first. Let’s just say he’s not a Gold Glove award candidate.

Players such as Dunn are better suited for the American League. The designated hitter was created with them in mind. Nationals General Manager Mike Rizzo definitely thought so.

Among the many organizational improvements Rizzo was determined to make, upgrading the Nationals’ defense was essential to his strategy. There’s nothing wrong with hitting the ball far, but Rizzo likes players who pick it up well, too.

Rizzo replaced Dunn with Adam LaRoche. Last season, LaRoche won his first Gold Glove, hit 33 homers and drove in 100 runs. Even Dunn said Rizzo got it right.

“Mike has done a great job, man,” Dunn said. “He had a plan, and he stuck to his plan. That’s what he’s supposed to do. “

It’s always easy to be gracious when you’re also in a good place mentally. Dunn is there with the White Sox. But the trip was rough.

The White Sox lured Dunn to Chicago with a four-year, $56 million contract. They weren’t counting on Dunn, a .240 hitter in his career, to suddenly have a high batting average. The White Sox figured Dunn would remain among baseball’s strikeout leaders. They signed him to hit homers.

Initially, the White Sox got much less than they expected. After spending his entire career in the National League (he also played for Cincinnati and Arizona), Dunn was lost in transition.

Although it’s not uncommon for players to struggle during their first seasons after switching leagues, Dunn was so overmatched for most of 2011 that some scouts thought he wouldn’t get it figured out again. In 496 at-bats, Dunn batted .159 with 11 homers. He drove in just 42 runs.

Dunn was never considered one of the Nationals’ most dedicated players in the weight room, and some around the game said his poor conditioning had finally caught up to him. All around Dunn, there was nothing but criticism.

“I never looked at it like I’d never get out of it. You can’t look at it like that,” Dunn said. “I’m not going to excuse you to death. What happened just happened. Obviously, it wasn’t good.

“But there were a lot of things that happened over that year. New team, new league, trying to come back from things too quickly . . . it all was part of it. If I had to do it over again, I would have done it differently. Then things wouldn’t have been like that.”

Change was needed.

Dunn worked hard on his conditioning. He rebounded with a 41-homer, 96-RBI performance last year, and has two homers in six games this season. Dunn didn’t play in the White Sox’s first game against the Nationals on Tuesday.

There’s no designated hitter in interleague series played at NL ballparks, and all-star Paul Konerko is Chicago’s everyday first baseman. Dunn was on deck to pinch-hit when Konerko flied out to end the Nationals’ 8-7 victory. Even if he doesn’t play a big role against the Nationals, Dunn plans to enjoy his return.

“Everyone was good to me here,” said Dunn, who was 0 for 4 with a strikeout and played left field Wednesday night. “So to see what they’re doing now, with a young team and veterans who are good players and good people, it’s good to see. It’s definitely good for baseball.”

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