Matthias and Upshall each added an assist for the Panthers, who won on the road for the first time since Jan. 26 and snapped a four-game losing streak. The Panthers and Buffalo Sabres are the only teams behind the Islanders in the Eastern Conference.
"Just a spark," Upshall said. "The guys were getting things going, and you just feed off the energy. You try to just bring your best game. This is a fun building to play in. You're seeing right off the bat it was going to be a rough game. Those are always fun to play. We stuck up for one another, we believed in the process, and tonight was a big win."
For the Islanders, who allowed four goals in the third period, it spoiled a two-goal effort from Thomas Vanek in what may have been his final game at the Coliseum wearing an Islanders sweater. The Islanders play again Tuesday night at the Winnipeg Jets to open a four-game road trip that also includes visits to the three Western Canada teams, but there's no assurance Vanek or defenseman Andrew MacDonald will be in a road uniform.
New York has won nine of 33 home games this season (9-16-8).
"If I was to stand here and tell you that we had major breakdowns, our D-zone coverage was terrible and that was the cause of their goals, then that's what I would tell you," Islanders coach Jack Capuano said.
The 2014 NHL Trade Deadline is Wednesday at 3 p.m. ET, and Vanek is one of the hot commodities rumored to be on the market after he declared his intention of becoming a free agent after the regular season. He has 21 goals and 53 points in 60 games with the Islanders and Buffalo Sabres.
Vanek ended an eight-game streak without a goal at 6:41 of the first after receiving a feed from Cal Clutterbuck and shooting it past Panthers goalie Tim Thomas for his 20th of the season. Goal No. 21 came 58 seconds later on an Islanders power play when he used a screen to beat Thomas up high.
Matthias got the Panthers, who had lost five straight road games, on the board at 18:15 of the second. Islanders defenseman Lubomir Visnovsky failed to clear the puck, resulting in a turnover at the blue line, and Matthias sent home a rebound past goalie Anders Nilsson, who got the start in the second of a back-to-back set for the Islanders.
"We seem to have a will to come back in those situations," Panthers coach Peter Horachek said. "We find ways to score. But we've got to stop putting ourselves in that 2-0 situation."
New York responded a minute later with Ryan Strome's second goal of the season. Kyle Okposo powered past his defender and moved the puck to the net. Parked in front, Vanek swept the puck to an open Strome, who put it past Thomas to allow the Islanders to take a two-goal lead into the locker room.
The Panthers' rally began at 3:16 of the third when Marcel Goc's shot from the point deflected off the stick of defenseman Matt Carkner. A minute and two seconds later, Matthias' second goal tied the game after he powered past MacDonald to beat Nilsson.
It marked the 12th time in 63 games the Islanders allowed a two-goal lead to slip away.
"Most of the time, if you don't bury a team, they'll get back in it somehow," Vanek said.
Frans Nielsen, who returned to the lineup Sunday after sustaining a broken hand Feb. 8, assisted on Vanek's second goal. Nielsen centered Anders Lee and Josh Bailey as part of Capuano's line adjustments before the game. Strome was moved to the second line between Michael Grabner and Okposo, and Vanek played with Clutterbuck and Brock Nelson.
The loss dropped the Islanders to 4-12-5 in their past 20 games at the Coliseum. It's only the third time in franchise history they've won as few as nine of their first 32 home games.
"Having a 3-1 lead going into the third, it's tough [to lose]," Strome said. "Obviously, everyone's got to play hard to the end. Regardless of what happens on the ice, you have to bounce back and find a way."