Lucas Duda of the Mets strikes out against the Nationals...

Lucas Duda of the Mets strikes out against the Nationals at Citi Field on June 16, 2017. Credit: Jim McIsaac

On Friday night in San Francisco, Sandy Alderson suggested that his Mets soon might be sellers, that stripping the roster of its marketable parts could be a looming inevitability.

Roughly 3,000 miles to the east, a few hours later, the Yankees designated Chris Carter for assignment, clearing first base for call-up Tyler Austin, presumably until Greg Bird makes it back from his bruised ankle, whenever that may be.

These were not unrelated events. The first-base dynamic between the Mets and Yankees will be something to watch closely in the weeks leading up to the July 31 non-waiver trade deadline.

It’s not very often that the New York rivals look to help each other in any capacity. But with pending free agent Lucas Duda among the Mets’ most desirable pieces, the Bronx could be the best landing spot, especially if the Royals (i.e. Eric Hosmer) remain in the playoff chase.

The struggling Carter was the first domino to fall, and with Joe Girardi campaigning all week for Austin’s promotion, the manager finally got his wish when Brian Cashman finally put him in pinstripes for Saturday’s game against the Rangers. Here’s what happens next: Austin gets to audition for a major-league job while the Yankees await Bird, who still is too sore from Monday’s cortisone shot to begin baseball activities.

Ideally, Cashman would like Austin to make everyone forget about the failed Carter experiment, then get a healthy Bird to resume taking aim at Yankee Stadium’s short porch on a regular basis. That way, the first-base problem is solved internally, Cashman saves his prospects for another piece — (cough) bullpen (cough) — and Bird assumes his rightful place among the Baby Bombers.

That’s the perfect scenario. The reality? The Yankees’ offensive production at first base has been abysmal. Their .599 OPS from the position ranks 29th overall, and only the Angels (.590) are worse. And Austin, after a stellar week at Triple-A Scranton/Wilkes-Barre, looked a tad anxious in Saturday’s 8-1 loss, striking out in his first two at-bats against the Rangers’ Austin Biben-Dirkx before bouncing into a 6-4-3 double play.

In his first time up, Austin whiffed on three off-speed pitches, swinging at each one. He pushed Biben-Dirkx to six pitches during this next trip to the plate, but after Didi Gregorius’ leadoff single in the seventh, Austin got impatient again in hacking at a first-pitch slider.

The Yankees’ concerns with Austin mostly had to do with him striking out once every 3.8 plate appearances for Scranton. But after he went 6-for-15 this week and homered in three straight games, they figured it was safe to jettison Carter. Now it’s up to Austin to reward Cashman’s faith after Saturday’s shaky debut.

“It wasn’t ideal,” Austin said. “I think I let the game speed up on me.”

He also narrowly avoided catastrophe when Pete Kozma collided with his glove, and apparently hyperextended his left wrist, when Starlin Castro tried to double up Kozma on a line drive in the fifth inning. Austin immediately took off his glove and shook his hand a few times before being checked out. Austin stayed in the game and later said he was OK, but Girardi wouldn’t completely clear him afterward.

“We’ll keep our fingers crossed and see how he is tomorrow,” Girardi said.

Maybe we’re too skeptical, but that sounded to us as though the manager was leaving the door open a crack to using someone else at first base in Sunday’s finale.

The same morning, Girardi stated unequivocally that Austin would be the everyday first baseman. But with the Yankees losing for the ninth time in 11 games, we can’t blame him for keeping his options open. He can’t afford a few days to let Austin settle in. It’s still only June, but there’s a feeling this malaise needs to end ASAP before the good vibes from the first two months are stomped out completely.

Austin will get an opportunity at first base. That’s for certain. Bird’s fragile status, however, makes him more of a question mark. He missed all of last season after having shoulder surgery and has played only 19 games this year, batting .100 (6-for-60) with one home run and 22 strikeouts in 72 plate appearances.

Injuries or not, that doesn’t make Bird sound like a sure thing. And right now, he’s definitely no Duda, who is hitting .258 (17-for-66) this month with five homers and a .931 OPS.

Despite both teams’ tendency to keep a wary distance from each other, neither Alderson nor Cashman harbors any objection to being trade partners.

The Yankees aren’t there yet. But they could be before too long.