Taylor Hall and Ryan Donato scored, and Arvid Soderblom made 36 saves for the Blackhawks (4-7-0), who were coming off a 5-2 win against the Florida Panthers on Saturday. Connor Bedard's goal streak ended at three games.
Chicago held a players-only meeting after the game.
“Essentially just being accountable and playing with the system we’ve installed through training camp and through the first few games of the season,” forward Corey Perry said of the meeting. “We do it in spurts, but we’ve got to do it for the full game. We had a good heart to heart, and we’ll move on.”
Blackhawks coach Luke Richardson was not part of the meeting.
“I wasn’t in on it, and that’s good,” Richardson said. “I think they hear enough from me before and during the game. If they feel there’s something that needs to be said, it usually goes a longer way when the leadership guys and whoever feels a need to speak speaks up.”
Hall gave the Blackhawks a 1-0 lead at 1:51 of the first period with his second goal in as many games. He scored on the rebound of a shot by Tyler Johnson from just outside the crease.
Mercer tied it 1-1 at 13:07 with a power-play goal. He took a pass from Erik Haula along the goal line, skated in and scored with a wrist shot over Soderblom’s left shoulder.
Willman, who was called up from Utica of the American Hockey League on Saturday, put New Jersey ahead 2-1 at 14:41, scoring on a breakaway after Blackhawks defenseman Kevin Korchinski couldn't control the puck at the blue line.