Not many people saw the Mets’ second-half surge coming, but Joe Maddon said he’s not surprised by it.

He pointed to their young hitters, such as Amed Rosario and Pete Alonso, and then singled out the biggest reason behind the fact the Mets are still in the playoff hunt — right behind Maddon’s Cubs.

“Their pitching,” Maddon said of the Mets on Tuesday at Citi Field, where the Cubs won 5-2.

And Maddon said it all came down to what they didn’t do at the trade deadline.

“Come on, it was wise to not get rid of those guys,’’ Maddon said of the fact they didn’t move Zack Wheeler or Noah Syndergaard — or Marcus Stroman — at the end of July.

“I read The Post, that’s all I read,’’ Maddon said. “I was reading this all year. Why would you trade arms like that just to make a move? They have some of the best arms, and if their bullpen pitches like they can, they’re as tough as anybody to beat.”

The Mets rotation has always been what’s intrigued Maddon.

“I’ve been on the Mets all year,’’ the manager said. “I thought they were better than their record indicated early on and now they’ve finally arrived at that point.”

He liked the addition of Stroman — and that they didn’t subtract anyone.

“They made their starting staff better,” Maddon said. “Their bullpen has gotten more straightened out. They have some young hitters that know what they’re doing at the plate. They’re interesting, man.”

Maddon is in the final year of his contract with the Cubs, and Theo Epstein, the team’s president of baseball operations, said he and Maddon agreed before the season to wait until the year was over to discuss his future.

The Cubs have had a somewhat rocky season and Maddon credited the rest of the NL with catching up to them since their World Series victory in 2016 more than his own team faltering.

“It’s a really good group,’’ Maddon said of his team when asked if there was pressure now that they are further removed from the championship.

“I don’t know that pressure is the right word,’’ Maddon said. “I’m a realist. Other teams are better, too. That’s the primary difference between ’16 and now. Our division has gotten better.”

And, according to Maddon, so have the Mets.

“I like their young players on the field a lot,’’ Maddon said. “Rosario, I’ve always been a fan. [Jeff] McNeil and then Alonso, from the beginning, and the [J.D.] Davis kid, I liked him from the beginning. [Michael] Conforto’s come back.”

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