CINCINNATI — The Mets’ search for catching help took an unexpected twist Tuesday, when Matt Harvey was traded to the Reds for Devin Mesoraco and cash.

The 29-year-old Mesoraco was scratched from the Reds starting lineup and available to play for the Mets, who cleared roster space by placing Todd Frazier on the disabled list with a strained left hamstring.

According to sources, the Reds will pay Mesoraco the remainder of the $13.125 million he is owed. The Mets will pay Harvey the $4.6 million he is still due.

Mesoraco, a former All-Star, was slashing .220/.289/.341 in 18 games this season for the Reds. He will give the Mets a veteran presence to bulk up the team’s depleted catching.

“I think we’re fortunate it happened to work out the way it did,” Mets special assistant J.P. Ricciardi said. “To be able to address one of our needs was something we were looking to do and we are pretty happy about that.”

An industry source told The Post on Tuesday that general manager Sandy Alderson and his lieutenants had been seeking a catcher as they spoke to teams interested in the former ace right-hander, who was designated for assignment by the Mets on Saturday.

As it stands, the Mets have struggled to receive production from the tandem of Jose Lobaton and Tomas Nido behind the plate with Travis d’Arnaud and Kevin Plawecki on the disabled list. D’Arnaud underwent Tommy John surgery that is expected to keep him sidelined for the remainder of the season and Plawecki is still not close to a return after sustaining a broken left hand last month.

Even a healthy Plawecki guarantees little, as there are questions whether he can handle the everyday grind behind the plate.

Mesoraco has battled various injuries over the last three seasons that have limited his playing time. His best season came in 2014, when he posted an .893 OPS and was named to the National League All-Star team.

“We get a veteran guy — a guy that when healthy has played really well,” Ricciardi said. “I think that brings a little more consistency to the position. Since we lost the two guys we have probably lacked a little of that, so I think he will help us in that area.”

The source added the Mets received “a lot” more interest in Harvey than they originally anticipated and fully expected a trade to materialize. The Padres were added to the mix on Tuesday, joining teams such as the Giants, Rangers, Mariners, White Sox and Orioles that showed interest.

The Giants had a need in their rotation after losing Johnny Cueto for at least a month to an elbow injury, but didn’t have the catching depth to satisfy the Mets. The Rangers had payroll flexibility, in addition to employing former Mets pitching coach Dan Warthen, but also weren’t viewed as having the catching depth to satisfy Alderson’s need.

Harvey was 0-2 with a 7.00 ERA in eight appearances this season for the Mets, but the Reds were willing to take a low-risk gamble that he can at least become a productive rotation piece.

The twist for Harvey is he will be attempting a career resurrection in a bandbox ballpark that isn’t kind to pitchers. Plus, the socially active pitcher has been dispatched to a city not known for its after-hours scene.

One Mets official, before the trade was announced, expressed optimism that a change of scenery could buoy Harvey, who has struggled since undergoing surgery for thoracic outlet syndrome in 2016. The Mets official noted that Harvey’s mind had wandered since his reassignment to the bullpen in recent weeks.

“Certainly it’s not like the stuff has disappeared,” Reds general manager Dick Williams said. “There is stuff there. The velocity has been good, we really like the changeup and it may be more of a pitch mix and approach than more of a mechanical change.”