NEW YORK -- The rain had just begun to fall in the eighth inning at Citi Field on Monday when the Mets loaded the bases with no outs, down by four runs. At that point, if their history of late comebacks was any indication, the Mets had the Cubs right where they wanted them.

Quickly, though, the rally dimmed, as New York made two quick outs. A left-handed pitcher, Brandon Hughes, was on the mound. In the dugout, manager Buck Showalter faced a choice: Darin Ruf or Mark Vientos.

• Box score

If ever there was a situation for the rookie Vientos, this was it. Called up over the weekend due to injuries elsewhere on the roster, Vientos carried promise as a new source of offense. His summer at Triple-A Syracuse had been memorable, with 24 homers and an .877 OPS over 101 games. More than that, Ruf was 0-for-September, mired in a 1-for-34 stretch dating well into the previous month.

Despite all those figures, Showalter chose Ruf, who lined out softly to shallow right. The inning ended, and Vientos went unused for the rest of the Mets’ 5-2 loss to the Cubs, which shaved their National League East lead back to a single game.

“I don’t know,” Ruf said when asked about the root of his struggles. “I’m just trying to have good at-bats. Sometimes, you need a little luck. Sometimes, you need some soft contact to fall. You certainly need hard contact to find holes. When the two don’t line up, you can get on a little stretch where you make more outs than you want.”

Afterward, Showalter referred several times to Ruf’s general acumen against left-handed hitters, whom he has hit at a .273/.369/.530 lifetime clip. That’s why the Mets acquired Ruf as the right-handed portion of the Trade Deadline haul, along with lefty platoon hitters Daniel Vogelbach and Tyler Naquin. The hope was that those three could reasonably approximate the production of a star-level player, with Vogelbach and Ruf starting most nights at designated hitter.

It just hasn’t worked out that way. Following hot starts to their Mets careers, Vogelbach and Ruf have cooled considerably for a team that came into Monday sporting the lowest collective DH OPS (.285) of any NL club in September. Vogelbach hasn’t homered since Aug. 22, and he recently went through an 0-for-14 skid at the plate. Ruf owns merely one hit over the last calendar month.

Put it all together, and it became easy to make a “why not?” argument for pinch-hitting Vientos against Hughes with the bases loaded in the eighth.

Showalter, who offered little public praise of Vientos before his promotion, was more interested in the opposite argument.

“Ruf’s been real good in that situation over his career,” Showalter said. “A lot more track record than some of the other people.”

Whether a different decision would have resulted in a different result is impossible to know for a team that did little to support starting pitcher Chris Bassitt, who “just wasn’t hitting spots” in his second-shortest outing of the season. Outside of James McCann’s RBI single in the fourth and Francisco Lindor’s solo homer with the game mostly in hand for the visitors in the ninth, the Mets couldn’t muster much off Cubs starter Javier Assad or a trio of relievers.

Over the coming days, the question may become why the Mets promoted Vientos in the first place if they didn’t plan to play him. With Eduardo Escobar riding a 10-game hitting streak and Starling Marte eventually due back from the injured list, the Mets aren’t likely to carry Vientos on their roster forever. So far, they’ve used him once in three games. If that trend continues, they may ultimately return him to the Minors without really knowing whether he’s ready to hit at this level -- not if his opportunities are sporadic while Ruf’s stay consistent.

“There haven’t been many better [than Ruf],” Showalter said. “We keep waiting. We think that Darin’s been really good in that spot for his career. It hasn’t been there for him lately.”