PHOENIX — The Yankees’ chances of winning the AL East are on life support.

Of greater concern is whether their bullpen meltdown Sunday was just a bad day or cracks emerging in a heavily worked unit.

Brent Headrick served up a grand slam to Nolan Arenado in the fifth inning, flipping the game on its head and all but wrapping up the Yankees’ spot in the AL wild-card series next week after an 8-4 loss to the Diamondbacks at Chase Field.

By dropping the series finale, a game they once led 4-1, the Yankees (89-66) fell to six games back of the Rays with seven to play. They will welcome the Rays to Yankee Stadium on Tuesday for a four-game showdown, needing a sweep to stay alive in the division race. One win by the Rays in The Bronx will secure them the AL East title.

“I feel like we let the last two slip away, which is tough to do right now,” Will Warren said. “But it’s coming down to the wire, and we got to keep winning, finding a way to win.”

Nolan Arenado (28) of the Arizona Diamondbacks runs the bases after hitting a grand slam off relief pitcher Brent Headrick (47) of the New York Yankees during the fifth inning at Chase Field in Phoenix, Arizona, Sunday, Sept. 20, 2026. Getty Images

If and when the division officially becomes out of reach, the Yankees would then turn their attention to securing the top AL wild card, ending Sunday leading the Red Sox by 5 ¹/₂ games, though Aaron Judge’s questionable status for that series because of a calf strain looms over everything.

Getting an early resolution on the division would allow the Yankees to give some of their overworked relievers (like Headrick) some rest, but first comes a Tuesday doubleheader against the Rays.

“We’re going to show up Tuesday and try to kick their butt,” manager Aaron Boone said. “Simple as that, and we’ll keep it simple.”

New York Yankees left fielder Heliot Ramos (34) celebrates his home run with first baseman Luis Garcia Jr. (26) during the third inning of a game against the Arizona Diamondbacks, Sunday, September 20, 2026, at Chase Field in Phoenix, Arizona. IMAGN IMAGES via Reuters Connect

In the meantime, Sunday’s loss — on the heels of Saturday’s walk-off win by the Diamondbacks (82-74) — was another regrettable one after third-inning home runs by Heliot Ramos, George Lombard Jr. and Spencer Jones off Corbin Burnes had staked them out to a 4-1 lead.

Then in the bottom of the fifth, Warren loaded the bases with one out, at which point Boone called on the reliable Headrick for his 79th appearance of the season — the second most in the majors.

Before Sunday, Headrick had inherited 50 runners this season and allowed only five of them to score. But after striking out the first batter he faced, Headrick walked Corbin Carroll to force in a run, which brought Arenado to the plate.

A New York Yankees fan watches during the ninth inning of a baseball game against the Arizona Diamondbacks, Sunday, Sept. 20, 2026, in Phoenix. AP Photo/Caitlin O’Hara

Arenado crushed Headrick’s 2-0 fastball just to the left of the left field foul pole, but then straightened it out on the very next pitch (another fastball), clobbering a grand slam to put the Diamondbacks ahead 6-4.

“I felt good, just lack of execution and falling behind hitters,” insisted Headrick, who was pitching for a second straight day.

“He’s been a dog for us all year,” Warren said. “It sucks, but obviously we rely on him, and he’s been really good for us all year, and he’s going to continue to be good.”

Headrick’s average fastball velocity was down again Sunday, as it has been for most of his outings of late, though his fastest pitch was the 94.2 mph heater — matching his season average — that Arenado drilled for the grand slam.

“He’ll be all right,” Boone said. “His stuff plays as long as he’s commanding the strike zone and using his slider and splitter effectively. Hopefully in this week, we can get him set up to be in a really good spot heading into the postseason.”

The Diamondbacks later added a pair of insurance runs off John Schreiber in the seventh inning, the first earned runs Schreiber has allowed as a Yankee, putting another serious dent in their chances of catching the Rays.

“That’s a tall task,” Boone said. “We got an off day [Monday], then come ready to play some baseball on a long day Tuesday and see where it goes.”