PHILADELPHIA — When last summoned, Mark Vientos knew that he should not get too comfortable.
Brought up at the end of April because Starling Marte was moved to the bereavement list, Vientos was told it would be a short stay, with Marte due back a few days later.
In those few days, Vientos went 3-for-7 with a walk-off home run in a win over the Cardinals, a moment that did not persuade the Mets to alter their plans.
This time is different.
Vientos was officially added to the roster and batted fifth Wednesday against opposing lefty starter Ranger Suarez.
Manager Carlos Mendoza declined to call his third-base spot a straight platoon between the righty-hitting Vientos and the lefty-hitting Brett Baty, but that appears to be how the club is trending.
The Mets will play the “matchups,” Mendoza said at Citizens Bank Park, “putting guys in a position to have success.”
The Mets’ offense has struggled at plenty of spots but particularly at third, a position from which they entered play with a collective .614 OPS that was the seventh worst among third-base groups in the majors.
Baty started the season hot and showed some of the potential that made him one of the game’s top prospects a year ago.
But he entered play with a cold bat that had logged just a .609 OPS and had struggled particularly of late, 1-for-22 with 11 strikeouts in his past seven games.
Mendoza called the 24-year-old into his office after Tuesday’s loss and told him that Vientos would be coming to play some third base in what amounts to a timeshare.
Vientos hopped in an Uber with Wednesday starter Joey Lucchesi and arrived hoping to bring power to the lineup and perhaps have staying power, even if he has learned to not look ahead.
He had one opportunity Wednesday, so that’s what he focused on.
“I don’t look into the future,” said the 24-year-old Vientos. “I”m just staying with the daily things that I got to do.”
For now, at least, those daily things mean killing lefties.
At Triple-A this season, Vientos has demolished opposing southpaws to the tune of a .393 average and 1.380 OPS.
Baty has not hit well against major league pitchers dealing from either side but has particularly struggled against lefties, against whom he entered play with a .172 average and .476 OPS.
Baty, though, has made marked improvements defensively and arguably has been an above-average third baseman in the early going of this season.
Vientos arrives with a spottier reputation but said he feels “really good, comfortable over there.”
Baty will have to learn to be comfortable at more spots than just third.
The slew of roster moves that included bringing up Vientos also involved designating utilityman Joey Wendle for assignment.
The Mets do not have a backup shortstop or backup second baseman on the roster, and Baty has been thrust into that role.
Baty took reps at both spots before Wednesday’s game — ground balls that were hit to him by Mendoza — and now will be an emergency option if something happens to Francisco Lindor or Jeff McNeil.
With a longer-term injury to either middle infielder, the Mets would find another infielder to plug in, but Baty is now on-call for in-game substitutions.
Asked how long the Mets could operate with such a strange roster makeup, Mendoza said they are taking it “week-to-week.”
“We feel comfortable where Lindor is physically, where McNeil is physically, especially for the next seven games or so that we got before [next Thursday’s] off day,” Mendoza said.
Part of the rationale for summoning Vientos’ bat and jettisoning a middle-infield glove is the fact the Mets are about to face several lefties.
After Suarez on Wednesday likely will come Miami’s Jesus Luzardo on Friday and Braxton Garrett on Saturday.
The Mets have opted, at least for now, to become less flexible defensively but more powerful offensively.
They do not have a middle-infield backup, and they have two third-base prospects who come with promise and no résumé of hitting major league pitching.
Perhaps they work well in tandem.
Perhaps one gets hot and runs with the spot. If neither happens, the Mets would have a problem.
“Thought it was a good opportunity for [Vientos] to get some playing time here,” Mendoza said.