All year, Luis Severino and Dellin Betances were the right arms the Yankees hoped would return in time to help them in the postseason.

And after Betances flashed some of his old stuff when he finally made his season debut on Sunday in Toronto after being sidelined by a shoulder injury followed by a lat strain, Severino did much the same for four scoreless innings in The Bronx on Tuesday night.

But in this Yankees season that has been defined by injuries, the good news wouldn’t last, as they learned Tuesday that Betances will be lost for the year with a partially torn left Achilles tendon.

The news put a damper on Severino’s return, as well as the 8-0 win over the Angels to open the Yankees’ final homestand of the season.

“Obviously, I’m heartbroken for Dellin and knowing he worked so hard to get to this point to be a factor for us and have him successfully debut for us,’’ manager Aaron Boone said. “And now this.”

Betances suffered the injury on a seemingly harmless hop on the mound after his outing Friday and he didn’t report a problem until Tuesday. And when tests showed an issue, Betances underwent an MRI exam that showed the injury.

For now, surgery hasn’t been recommended, but the Yankees won’t have him in the playoffs.

Afterwards, a Yankees team that’s practically numb to getting bad injury updates, acknowledged the hole the loss of Betances would leave, but pointed to their resiliency that will be tested once again.

Boone called Betances “one of the handful of best relievers in the game for several years now. We know how great he is and what a difference-maker he is, but we certainly have the people here to continue to have our bullpen be a strength.”

The return of Severino — and how he looked on the mound — softened some of the blow, as the Yankees inched closer to a playoff berth, which could come on Wednesday.

There had been encouraging signs in Severino’s three minor league rehab starts, but the biggest question was whether Severino would have his command — and have enough time to fine-tune his pitches in time for the playoffs.

Early indications were good, as Severino routinely hit the mid-90s throughout the 67-pitch outing. He topped out at 98 and made some of his best pitches when he needed to.

He took the mound and immediately fired a 93 mph fastball to Brian Goodwin, but the center fielder worked a 12-pitch walk to start the game. David Fletcher followed with an 0-2 flare to left to give the Angels runners on first and second before Kole Calhoun bounced back to the mound for a force-out.

With runners on the corners, Severino got Albert Pujols to ground into a double play to end the inning.

Severino cruised through much of the rest of his start and the offense provided two runs in the second and six more in the fourth, capped by a three-run homer from Gleyber Torres — his team-high 38th of the year.

Severino gave up two hits and a pair of walks, while striking out four, in four innings.

“I loved how he stayed within himself,’’ Boone said.

He could make two more starts before the playoffs begin and it remains to be seen if he gets built all the way back up to 90-100 pitches, but looks ready to provide a boost to the pitching staff just in time for the playoffs.

“We need [Severino] where we’re going,’’ catcher Austin Romine said. “He’s pitched in big games for us and we look forward to him pitching some more of them.’’

“I felt very comfortable out there,’’ Severino said. “I’ve been looking forward to this since spring training. It’s been a long time and a long road back. I’m here now and I’m healthy and can help my team.”

They’ll need more from a staff that just days ago believed it had Betances ready for October, only to have him yanked away again.