CINCINNATI — Cuban defector Aroldis Chapman is bringing his 105 mph fastball to the big leagues.

The Reds plan to call up the hard-throwing lefty before their game Tuesday night against the Milwaukee Brewers, trying to strengthen their bullpen for a playoff push in September and beyond.

By adding him in August, the Reds will make him eligible for the postseason — and unleash him on opposing hitters who have never seen him.

The NL Central leaders had a five-game edge over St. Louis heading into Tuesday’s games.

“I think Dusty (Baker) will ease him into a role until he gets his feet on the ground, he gets accustomed to pitching up here,” general manager Walt Jocketty said in an interview. “Then depending on how he does, we’ll see how the role develops.”

The 22-year-old Chapman signed a six-year, $30.25 million deal with Cincinnati in January. He was in the competition for the fifth starter’s spot during spring training until he was sidelined by back spasms.

The Reds sent him to Triple-A Louisville to start the season. He got mixed results, throwing a lot of pitches to get through five innings. He went 5-5 with a 4.11 ERA in 13 starts.

Cincinnati has plenty of starters, but decided to see if Chapman could help the Reds out of the bullpen this season. They moved him into a relief role at Louisville last month and he was even better, going 4-1 with a 2.40 ERA in 26 relief appearances.

His fastball was clocked at 103 mph as a starter. Jocketty said he’s been throwing consistently harder as a reliever, hitting 105 mph recently. He has struck out 49 in 30 relief innings.

“We felt with his stuff, if you shorten the game more he should be successful,” Jocketty said. “That’s why we put him in there for now. We’ll get him back to starting next year.”

Chapman has handled his many adjustments — new country, new culture, new baseball team — without much trouble. Jocketty thinks he’s ready to handle the pressure of making his major league debut in the middle of a pennant race.

“That’s why we left him down there a little bit longer, to get more experience in the bullpen,” Jocketty said. “And he’s adapted really well to it. He actually enjoys it.”