TAMPA, Fla. -- The New York Islanders were mentally prepared for Game 1 of their Stanley Cup semifinal series. The Tampa Bay Lightning were not.

"Our work ethic was there. Our compete [level] was there. Our minds weren't there," said Lightning coach Jon Cooper, whose team lost 2-1 on Sunday afternoon. "Some of our decisions were poor. That's what happens when you get this deep into the playoffs. You have to have everything working in unison and we just weren't there tonight."

The Lightning looked disjointed in Game 1. Their passes didn't connect. They weren't on the same page offensively.

Most importantly, they failed to protect the puck against one of the most adept defensive teams in the NHL. Tampa Bay had seven giveaways in the game, including one by Steven Stamkos that led to Mathew Barzal's opening goal in the second period. The Islanders, by contrast, had only one giveaway.

"We knew it was going to be tight. On the first goal, I was trying to make a play, and you see what can happen. They can go the other way and score," Stamkos said. "We knew it was going to be extremely tough. We've been in this position before. There's definitely no panic in this room."

This was the first meeting between the Islanders and Lightning since last summer's Eastern Conference final, played inside the Edmonton "bubble." The Lightning won that series in six games. Islanders coach Barry Trotz saw similarities between this game and some of the ones in that series.

"Both teams are pretty much the same as they were last year. Systematically, we're pretty similar. Pretty well what we expected, and in some ways that was good," Trotz said.

The Islanders couldn't have scripted a better Game 1 on the road. They were physical from the start, as Matt Martin and Barclay Goodrow earned matching unsportsmanlike conduct penalties just eight seconds into the game. They built a 2-0 lead on goals by Barzal and defenseman Ryan Pulock, who beat Andrei Vasilevskiy (29 saves) at 5:36 of the third period. They got a strong 30-save performance from goalie Semyon Varlamov.

Best of all for the Islanders, they earned the first three power plays of the game before the Lightning -- owners of the playoffs' best power play -- had one. Tampa's lone power-play goal by Brayden Point came on a 6-on-4 late in the third period, with Vasilevskiy pulled.

"We took a couple of penalties early in the game. We had a pretty good start and it sucked the momentum out," Stamkos said.

The Islanders didn't allow the Lightning many high-danger scoring chances in the attacking zone, limiting them to six through the first two periods at 5-on-5 while earning nine high-danger chances of their own.

But Cooper felt this was less due to a lack of effort by the Lightning than a lack of execution.

"We weren't using our heads like we normally do tonight," he said, adding that he didn't feel the Islanders' defenders had frustrated his team. "It's frustrating to lose. That's the frustrating part. But this is no different than the team that we beat in the bubble. We just made too many mistakes. The unforced errors. Managing the puck is a big thing against this team, and they managed it better than we did. And they got one extra break."

Game 2 is Tuesday night.