After not winning a Stanley Cup Playoff series from 1994 to 2015, the New York Islanders advanced to the Eastern Conference Second Round for the second time in four seasons.

The Islanders completed a four-game sweep of the best-of-7 Eastern Conference First Round against the Pittsburgh Penguins with a 3-1 win at PPG Paints Arena on Tuesday.

New York, which outscored Pittsburgh 14-6, awaits the winner of the first-round series between the Washington Capitals and Carolina Hurricanes, which the Capitals lead 2-1. Game 4 is at Carolina on Thursday (7 p.m. ET; NBCSN, SN, TVAS, FS-CR, NBCSWA).

Here are 5 reasons the Islanders advanced:

[RELATED: Complete Islanders vs. Penguins series coverage]

1. Stifling defense

After surviving an up-and-down style in a 4-3 overtime win against the Penguins in Game 1, the Islanders reverted to what made them successful over the course of the regular season, when they allowed 191 goals, the fewest in the NHL. Center Sidney Crosby finished the series with one assist for the Penguins; center Evgeni Malkin and forwards Jake Guentzel and Phil Kessel combined to score three goals.

"We just did our best to kind of bend, but not break," Islanders forward and captain Anders Lee said. "We were prepared as best we could and ready for this playoff hockey. I think we've proven that a little bit."

Video: Islanders advance with sweep of Penguins

2. Eberle steps up

No one on the Islanders has benefited more since coach Barry Trotz altered lines in mid-March than forward Jordan Eberle, who was reunited with center Mathew Barzal after the two experienced success together last season. Eberle scored in each of the four games against the Penguins after having five goals in the final seven games of the regular season.

"[Barzal's] finding me in areas where I'm able to finish plays off," Eberle said. "Since they put [Barzal] and [Lee] and me together, the puck's been going in a lot more. It seemed like we scored every game. That's obviously huge, you want to continue to play that way and moving into the postseason, you want it continue, and that's happened."

3. Lehner goal-den

The Islanders really could have gone either way in regard to a starting goalie in this series, considering how identical the numbers were between Robin Lehner (25-13-5 during the regular season with a 2.13 goals-against average, .930 save percentage and six shutouts) and Thomas Greiss (23-14-2, 2.28 GAA, .927 save percentage, five shutouts).

Trotz opted to go with Lehner, who was sensational in the series, winning all four games with a 1.47 goals-against average and .956 save percentage.

"We were able to manage the ups, which was the key, I think," Lehner said. "When they really threw everything at us, we played simple, we kind of made it really frustrating for them. A lot of credit to the guys."

Video: Lehner's stellar play leads Islanders to Round 2

4. Isn't that special

The Penguins were expected to have the edge in special teams given the surplus of weapons on their power play, but the Islanders allowed one goal in 11 shorthanded situations. Their penalty kill went 3-for-3 in Game 4 to help complete the sweep.

"Our penalty kill found ways to keep the puck out of the net," Trotz said. "When all else failed, Robin was fantastic."

5. Coach class

Trotz has done a masterful job in his first season as Islanders coach, not only fixing what was the worst defense in the NHL but creating an identity each of his players has clearly bought into. Trotz did not shy away from rolling four lines against Pittsburgh, and the defensive structure he has instilled limited the amount of quality chances Pittsburgh could generate.

"Just a group effort, which we wouldn't expect anything different from the Islanders," Trotz said. "We said we wanted to fix a couple of things, we wanted to play a certain way, we talked about culture and identity, and we tried to create that with what we felt we had."