NEW YORK -- The Mets lost two key members of their pitching staff on Sunday, placing left-hander Steven Matz and right-hander Dellin Betances on the injured list. The team promoted Franklyn Kilome and Drew Smith to fill their spots.

That Matz went on the IL with left shoulder discomfort was inevitable for the Mets, who sent him for an MRI on the shoulder early last week. Following a period of treatment, Matz returned to the mound Saturday, pitching a scoreless inning against the Yankees before complaining of further shoulder discomfort.

"It is a surprise because I was feeling so good," Matz said of his season progression. "Coming in, I was feeling so good. Even when I was struggling with my results, my arm was feeling really strong and healthy. So I'm pretty bummed about it, definitely."

Also in that game, Betances uncorked a walk-off wild pitch, inflating his ERA to 6.10. Betances has struggled all season with his velocity, which has fallen from 98 mph from 2016-18 to 93 mph this season. He has also walked 6.1 batters per nine innings, more than 50 percent higher than his career rate.

On Sunday, the Mets revealed that Betances is dealing with right lat tightness, a similar injury to the one that shut him down during his rehab from a shoulder issue last June. Betances missed nearly all of that season, before returning and partially tearing his left Achilles tendon during his only appearance for the Yankees.

Both Matz and Betances will see a doctor on Monday for further evaluation.

The Mets had been counting on Betances to be a key part of their late-innings mix after signing him to an incentive-laden one-year deal worth a guaranteed $10.5 million, with options for future seasons. When Betances struggled to find his old velocity in Spring Training, he vowed to be right by the regular season. But Betances' velocity never climbed, as he struggled with both his control and his ability to put away hitters with two strikes.

"I've got to find a way ... to make it work," Betances said after taking the loss Saturday at Yankee Stadium. "I've got to learn to pitch with what I have right now."

Also struggling throughout the early season was Matz, whose 14.66 ERA over three August starts prompted the Mets to demote him to the bullpen. Before Matz could appear in relief, however, he began experiencing abnormal shoulder soreness, precipitating an MRI. When that test came back clean earlier this week, Matz rehabbed and threw a bullpen session, before returning to the mound for a scoreless inning Saturday.

Afterward, he complained of renewed soreness.

"I guess maybe I wasn't ready to ramp it up yet," Matz said. "I felt a little discomfort again."

Whenever Matz returns from the IL, he is ticketed for the bullpen, though his ultimate goal is to earn his way back into the rotation.

"I'm not going to pout," Matz said. "I'm just going to work hard and try to help the team win in that capacity. That really was my mindset."

From the trainer's room
Mets third baseman J.D. Davis departed Game 2 of Sunday’s seven-inning doubleheader after six innings due to left hip discomfort. Rojas said he was unsure if the issue was related to the 99-mph fastball that struck Davis on the left side in Saturday’s game, but the manager does not consider the issue serious. Davis is day-to-day, and he could return to the Mets' lineup as soon as Monday.

Infielder Eduardo Núñez, who has been sidelined since July 26 due to a hyperextended left knee, has been working out at the Mets' alternate training site in Brooklyn. According to manager Luis Rojas, Núñez is progressing extremely cautiously due to a history of knee trouble.

"I'm in touch with him and he tells me all the time how hard he's working," Rojas said. "So he is progressing. He's still rehabbing. His timeline is uncertain still."

Player pool addition

The Mets added eighth-ranked prospect Mark Vientos to their 60-man player pool on Sunday, sending him to their alternate training site for live reps in the absence of a Minor League season. The move also makes Vientos eligible to be included in trades prior to Monday's deadline.

The Mets now have all six of their Top 10 prospects in their player pool, including the entire Top 5: Ronny Mauricio, Francisco Alvarez, Andrés Giménez, Brett Baty and Matthew Allan.