LONDON -- The Mets were faring well enough in their London Series opener when, with two outs in the fourth inning, Phillies shortstop Edmundo Sosa lifted a lazy fly ball in the general direction of the Strait of Dover. Starling Marte drifted toward it, appeared to settle under the ball, and then … simply stopped.

For Sosa, it went down as an RBI single in the box score. For the Mets, it became a four-alarm fire. The next batter, Whit Merrifield, hit a three-run homer off Sean Manaea to give the Phillies a 5-1 lead, and New York didn’t threaten much from there in a 7-2 defeat.

“It was all just such a blur,” Manaea said.

The problem, Marte later explained through an interpreter, was that he didn't see the ball until it was too late. London Stadium, which was built for the 2012 Summer Olympics and has housed the West Ham United soccer club since 2016, features a partial roof ring around the seating bowl. Center fielder Harrison Bader called the architectural quirks “definitely a little different than I’m used to,” while lauding the crew that converted this stadium into a baseball field.

Specifically, both Bader and Marte referred to the position of the sun, which -- due to the ballpark’s orientation, as well as a sun that doesn’t set until after 9 p.m. this time of year in London -- lingered in their field of vision throughout the early innings.

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“We knew it was tough to see those tweener balls with the white overhang,” Phillies second baseman Bryson Stott said, noting that his team practiced tracking fly balls Friday during its pre-series workout. “We knew hitting the ball to the outfield you had to run because they might not see it. A couple of our guys said they lost it for a second and things like that.”

Marte can now count himself among them, costing the Mets a chance to stay competitive in the London Series opener. By the time the fourth inning ended, the Phillies had scored six times -- all of them earned runs charged to Manaea.

“It was just difficult to see,” Marte said. “You kind of had to wait for the ball to get out of that shadow.”

For Marte, a standout defender throughout his career, such outfield misplays have become all too common. But the shift hasn’t happened overnight. After amassing +15 OAA as a center fielder from 2017-21, which was tied for 29th in the Majors among 137 qualified outfielders, Marte joined the Mets on a four-year, $78 million contract. Even in the opening months of that marriage, however, club officials were tepid enough in their assessment of Marte’s defense to shift him to right field, naming Brandon Nimmo their starter in center instead.

Since then, Marte’s defense has only declined:

2022: -2 OAA
2023: -6 OAA
2024: -8 OAA

Those numbers, as Mets manager Carlos Mendoza noted, are almost entirely due to Marte’s diminished range, particularly on plays to his left. His 2024 OAA total is the worst among any Major League outfielder, yet his arm strength remains elite, as Marte has proven with five outfield assists -- tied for second in the Majors.

“He’s working really hard,” Mendoza said. “Obviously the metrics, especially range-wise, [aren’t good]. But his arm has won some games for us.”

Before the London Series, Marte sat out one game due to a right knee injury that he and Mendoza both classified as minor. Last year, Marte missed the final eight weeks due to post-surgical groin discomfort that, in retrospect, he says affected him all season. But at age 35, Marte reported to Spring Training as a healthy player. He has appeared in 57 of the Mets’ first 63 games, putting him on pace for his highest total since 2015 -- still the only full, healthy season of Marte’s career.

So if injuries aren’t the issue, what is? Marte pointed to a more correctable problem: his positioning in right field, which he says he plans to discuss with Mets coaches. (On Sosa’s ball, Marte was shaded toward right-center field, which is typical when defending against a right-handed hitter.)

While such problems might be correctable in the future, that didn’t ease their immediate sting. Whatever the cause of Saturday’s misfortune -- the roof, the sun, his positioning or some other, unseen force -- the bottom line is Marte did not make the play.

“You knew something wasn’t right,” Mendoza said. “Sure enough, it was just them having a hard time picking the baseball off the bat.”