"We call him Benjamin Button," Bishop said, referring to the 2008 movie character who gets younger as he ages. "Sergei keeps finding ways to help us win, that's for sure."
Gonchar's go-ahead goal with 1 minute left was part of a four-goal, third-period outburst by the Senators, who rallied from a two-goal deficit and earned a 5-3 victory over the Islanders on Tuesday night.
The veteran defenceman, who will turn 39 next month, also had two assists.
"I'm just glad we got the two points and kept pace in the conference," Gonchar said.
Gonchar's second goal of the season came on a blast from the point to make it 4-3, and Guillaume Latendresse added an empty-net goal to seal the win. Jakob Silfverberg and Zack Smith scored in a 68-second span early in the third period to tie the game after the Islanders led 3-1.
Ottawa (16-8-6) has won three straight.
"We told ourselves after the second period that we weren't out of it, that we needed a quick goal," said Bishop, who made 26 saves. "We got two quick ones, and then Sergei found a way to score the big one. We have great leadership in this room and he's a huge part of it."
New York's Josh Bailey had scored the go-ahead goal 14 seconds into the second period, and Lubomir Visnovsky extended the Islanders' lead to two goals..
It was the second straight game in which the Islanders squandered a third-period lead. They led Florida 3-0 on Saturday before the Panthers tied it. But Casey Cizikas scored the winner for New York with seven minutes left.
"It's disturbing," Islanders coach Jack Capuano said. "We put ourselves in this situation."
Keith Aucoin appeared to give the Islanders a 4-3 lead at 7:22, but the goal was disallowed because he kicked the puck past Bishop.
Bishop also stopped Aucoin, who scored New York's first goal, on a sharp-angle shot from the left corner late in the third.
Ottawa's Matt Kassian opened the scoring at 6:23 with his first goal of the season and first with the Senators when he redirected Gonchar's slap shot past Nabokov.
Aucoin tied it with a wrist shot past Bishop at 17:53 of the first, netting his fifth of the season.
Bailey's third goal, on a backhand that skittered past Bishop, put the Islanders up 2-1. It was the 50th career goal for Bailey, a first-round draft pick by the Islanders in 2008. Visnovsky put the Islanders ahead 3-1 with a power-play goal at 11:46 of the second.
The Islanders (13-13-3) began a four-game homestand after road wins over Tampa Bay and Florida. New York is only 5-9-2 at home. They are three points out of a playoff spot in the Eastern Conference.
It was the third and final regular season meeting between the clubs. Ottawa won 3-1 at home on Feb. 19, and the Islanders earned a 3-2 shootout win at home on March 3.
"We made some adjustments and got momentum on our side," Senators coach Paul MacLean said. "The character in our room was evident in the third period. You have to play 60 minutes in this league."
The Senators also lost defenceman Marc Methot to an apparent right leg injury after a hard, clean check from the Islanders' Brad Boyes in the second period.
The Islanders have been tied or ahead in the third period in 23 of 29 games this season and are 13-7-3 in those contests.
NOTES: Ottawa forward Milan Michalek had knee surgery and is out indefinitely. The Senators were also without G Craig Anderson (ankle), defencemen Erik Karlsson (Achilles) and Mike Lundin (concussion), and forwards Jason Spezza (back) and Dave Dziurzynski (concussion). The Islanders were missing Matt Carkner (lower body) and forwards Michael Grabner (shoulder) and David Ullstrom (groin). ... Daniel Alfredsson played his 1,160th game for the Senators. He is the longest serving captain in the NHL (appointed in October 1999). His assist on the goal by Latendresse was the 1,100th point of his career.