HARRISON, N.J. — The warning signs were there for New York City FC coach Ronny Deila long before Eduardo Vargas snuck in a rebound in second-half stoppage time to lift Tigres UANL to a 1-0 win in the first leg of the Concacaf Champions League quarterfinal Wednesday night at Red Bull Arena.

There were the multitude of chances in the first half, but perhaps more puzzling for the first-year coach was how NYCFC changed in the second half.

“The second half, as I said, why we stopped playing the way we do on the ball?” Deila said. “We’re still fighting and working together as a team, but we need to take more chances on the ball, so they have to get troubled, so they have to run after us. And that didn’t happen in the second half. It was too little on the ball.”

That allowed Tigres to get more into the game, and eventually, come away with a critical away goal at the death.

So what happened after halftime?

“I think a little bit is too much transition,” midfielder James Sands said. “Every time we did win it, we were just going, going, going. Sometimes we just have to put our foot on [the ball] and slow it down a little bit. That will give us the ball more and we’re not defending for so long.”

As for the opening 45 minutes, it played out exactly how Deila would have hoped and almost the same way it did against AD San Carlos.

On Wednesday night, though, those chances weren’t converted into goals.

“We get the ball in central, get it wide, put up the wingers one-v-one, get chances,” he said. “The way we played was fantastic. That’s something we have to continue.”

The difference, Deila said, was NYCFC were too rushed in the attacking third when those chances came against Tigres.

“I think we have to be more calm. In this situation, we have more time than we think we have. … I think we are a little bit stressed in these situations,” Deila said. “I think that’s the main part. The worse is if the chances [don’t come].”

The pragmatic Sean Johnson didn’t pin the defeat on any one thing, nor was he too concerned on the why. He’s more about the bottom line and when the final whistle blew, NYCFC just didn’t get the job done in their home leg.

“I think we could have done a lot of things better on the night,” Johnson said. “But at the end of the day we have to come away with a result.”