"I know the guys were really happy and I was just celebrating there in the corner," Mercer said. "The fans got up, the building erupted and it was a great feeling for me."
Damon Severson, Jimmy Vesey and Pavel Zacha scored, Ryan Graves had two assists, and Jonathan Bernier made 27 saves to help the Devils win their second straight game to start the season.
New Jersey center Jack Hughes had an assist before leaving the game with 1:06 remaining in the first period with an undisclosed injury. He left on his own power after being checked into the boards and off his skates by Kraken defenseman Jeremy Lauzon while trying to retrieve a puck in the corner.
"He's day to day right now," Devils coach Lindy Ruff said. "He'll be evaluated tomorrow, and we'll see where he's at. I've had my share of shoulder injuries. I know when you stick your arm out, something bad can happen, sometimes."
Riley Sheahan and Jared McCann scored, and Yanni Gourde had an assist in his first game for the Kraken, who lost their third straight. Joey Daccord made 29 saves after being recalled from Charlotte of the American Hockey League on Tuesday.
"It's pretty tough to come in with new linemates, new team, new everything, but we did a good job of simplifying everything, just going north and deep," Gourde said. "It didn't work, we didn't win, but we had some good looks and we can build from there."
Gourde, selected by Seattle in the NHL Expansion Draft on July 23 after helping the Tampa Bay Lightning win the Stanley Cup the past two seasons, had offseason surgery on his left shoulder and was expected to be out for the first two months of the season. The forward missed the first week.
Mercer gave the Devils a 1-0 lead when the center scored on a one-timer from the bottom of the left face-off circle to finish a 2-on-1 with Tomas Tatar at 5:02 of the first period.
"It's great," Mercer said. "I like to be an offensive player, and getting the assist (in the 4-3 overtime win against the Chicago Blackhawks on Friday) and the goal this time, it was a good feeling," Mercer said. "It's just another hockey game, but it's obviously nice to get that one out of the way and just focus on the next game."
Severson, who missed the season opener with a lower-body injury, scored on a backhand from the slot to make it 2-0 at 6:42.
"I'm usually better on the defensive side of the puck, but it was nice to see that one go in," the defenseman said.