EAST RUTHERFORD, N.J. — Jets fans were pumped for Sunday’s home-opener. And rightfully so.

The Jets were coming off a commanding win in Detroit, in which quarterback Sam Darnold had shown some great signs of progress.

But it didn’t take long for that positivity to drain out of MetLife Stadium.

The Dolphins beat the Jets 20-12, cruising to a 20-0 halftime lead and holding on for the win.

The Jets had talked all week about handling prosperity, and that they hadn’t accomplished anything yet after the win over the Lions. But it didn’t matter, they still came out played atrocious against a Miami team that was hardly impressive.

The Jets squandered opportunities at every turn. The offense wasn’t good enough. The defense made silly, crippling mistakes.

And now the Jets have only a few days to fix it before the play the Browns in Cleveland on Thursday night.

Darnold’s day

After all they hype from the first day, it wasn’t surprising to see Darnold fall to earth against the Dolphins.

He looked like a rookie, completing 25 of 41 passes for 334 yards, a touchdown and two interceptions. His first-quarter pick cost the Jets a touchdown. Darnold was looking for receiver Quincy Enunwa on a slant route on second-and-6 from the Jets 39. Darnold was locked in on Enunw and never saw Miami safety T.J. McDonald who was waiting and baiting him.

Darnold made the throw and McDonald stepped in front of it for an easy interception, returning it down to the Jets’ 15-yard line. Miami needed only three plays to score, with running back Kenyan Drake punching it in for a six-yard touchdown on third-and-1.

Darnold certainly shoulders some of the blame, especially on that pick. He missed several open throws. But a lot of this was on the offensive line. After looking so good in Detroit, the unit struggled to give the rookie time to throw on this day.

Missed opportunities

There are several missed opportunities that the Jets will surely be kicking themselves for as they review the film.

At the end of the first half, Darold hit Terrelle Pryor for a 44-yard gain to get all the way down to the Miami 15. Down 20-0, the Jets had their golden opportunity to get back into the game.

But they couldn’t get into the end zone. Darnold missed a wide open Quincy Enunwa in the back of the end zone on first down, and on second down, Chris Herndon couldn’t get into the end zone and time expired without anything to show for it.

Early in the third quarter, the Jets scored a touchdown and then Jordan Jenkins immediately forced and recovered a fumble — sacking Ryan Tannehill — to give the Jets the ball at the Miami 12-yard line.

But on first down, Darnold overthrew Terrelle Pryor in the back of the end zone and was intercepted by Xavien Thomas who got both feet in for a touchback.

Those two missed chances were the most glaring, but there were others.

Costly mistakes

Stupid penalties continue to cost the Jets.

Late in the first half, they had Miami stopped when Leonard Williams and Avery Williamson sacked Tannehill on third down. But Morris Claiborne was called for a holding penalty. Miami went on to score on that drive and take a 20-0 lead.

And in the third quarter, the Jets once again sacked Tannehill, only to have it wiped out when Buster Skrine was called for a holding penalty completely away from the play.

But worst of all might have been another third-quarter sequence.

The Jets drove down into Miami territory and had first-and-10 from the 25. But then Brian Winters and James Carpenter were called for back-to-back false starts on first down.

The Jets never could recover and had to settle for a field goal when they needed more.

Defense impresses, but…

The Jets’ defense had another strong day, forcing two turnovers and sacking Tannehill four times.

Jamal Adams had a nice day. He had a strip sack in the first quarter and a touchdown saving tackle. Henry Anderson continued to put pressure on the quarterback.

By the end of the first half, the defense looked worn down — and the offense is to blame for that, because they couldn’t stay on the field to give their defense a break.

But that’s no excuse for the silly, costly penalties.

Late in the fourth quarter, the defense could have given the Jets one last shot trailing 20-12. But they couldn’t get off the field. The most glaring play: they allowed Frank Gore to catch a pass and pick up the first down on third-and-19.

No run game

In the end, it was an bad day for the offensive line which had looked so good against the Lions. The Jets rushed for only 42 yards on 19 carries and Robert Quinn got into the backfield repeatedly, making life tough for Darnold.

The Jets won’t often face a pass rushing comibination as effective a Quinn and Cameron Wake. But they need to clean things up, quickly.

Email: vasqueza@northjersey.com