ST. PETERSBURG, Fla. — Manager Aaron Boone kept the lineup intact from Game 1 — most notably keeping a struggling Ryan McMahon at third base — in part because he wanted “to prioritize the defense,” he said a couple of hours before Monday’s first pitch.

It took two pitches from Cam Schlittler for that decision to backfire.

McMahon made the first error, a drip that became a flood, in an embarrassing 5-2 loss in Game 2 to the Rays in which the Yankees defense was charged with four errors and probably should have been charged with more.

The problems started on the second pitch Rays leadoff hitter Yandy Díaz saw, chopping a grounder toward McMahon. The normally sure-handed veteran, perhaps misjudging the springs on the Tropicana Field turf or an infield dirt that played fast, missed on his backhand attempt. The ball skittered past him, McMahon raising his palms wondering what had just happened. Two more errors followed in an inning in which the Rays scored an unearned run.

McMahon did not make a second mistake in the field, but he also did not atone at the plate. He popped out in the third inning, managed a walk (that did not lead to a run) in the fifth and then was subbed out for pinch hitter Paul Goldschmidt in the eighth.

In four postseason games, McMahon is 1-for-7 — the lone hit an infield single — with two walks and played despite entering the night 1-for-14 with three walks in his career against Tampa Bay starter Freddy Peralta.

Asked about sticking with McMahon, Boone indicated that he considered starting Anthony Volpe at third base, but didn’t want his second career start there to be on the bouncy turf in a playoff game. Boone also insisted José Caballero was “very much in play” — and has been every day of the playoffs, he said, “but I just like his versatility and presence off the bench, too.”

Caballero, a spark plug who had appeared in only one game this postseason before Monday (as a defensive replacement in Game 2 of the wild-card series), played the role of good soldier.

“Everyone wants to be in there, but that’s why we have a manager and he’s the one making decisions,” Caballero said before entering as a defensive replacement at third base. “Just waiting on my time and trying to stay active and prepare for the moment that I get the call and try to help the team.”

Caballero was 0-for-2 in his career against Peralta, but unlike McMahon, can change the game with his speed and is more of a contact threat. He hit .233 with a .666 OPS against righties this season while McMahon hit .218 with a .662 OPS.

Boone said if the Rays start a left-hander in this series (they had not yet announced their rotation beyond Game 2, but Ian Seymour would be the only lefty option), Caballero would start at third.