Already the first Japanese-born player in the NHL, Fukufuji was lifted less than two minutes into the second period after Jim Slater's deflection gave the Thrashers a 3-1 lead. He stopped only six of nine shots.
"It was pretty bad," Fukufuji said. "I can play better."
Los Angeles closed to 3-2 when Tom Kostopoulos scored just over two minutes into the third period. But Hossa, who will represent the Thrashers at the All-Star Game next week, found the net two more times to turn it into a runaway.
He has 29 goals for the season.
"This feels good," Hossa said. "We finally made it easy on ourselves."
Kari Lehtonen turned aside 28 shots for first-place Atlanta, which won its second in a row after a five-game losing streak. Los Angeles is mired in a five-game skid.
"It's kind of fun winning with a big margin, rather than by one or two goals," Lehtonen said. "We've been playing very well the last few weeks, but there's always been one bad period. Tonight, we played solid for three periods."
Fukufuji, recalled from the minors after the Kings' top two goalies went down with injuries, played the third period of a 6-5 loss to St. Louis on Saturday night.
He started against the Thrashers and was staked to a quick lead when Derek Armstrong sped into the Atlanta zone and passed in front to Frolov, who managed to beat Lehtonen off a bouncing puck before defenseman Greg De Vries could tie him up.
But Hnidy quickly tied it with a shot that had no business going in. The defenseman circled near the blue line and fired a shot toward Fukufuji, who had a clear look at it but let the puck deflect over his shoulder for the softest of goals.
Hossa scored off a rebound later in the first to put the Thrashers ahead to stay, and the Kings switched goalies after Slater's slight deflection on a shot by Ilya Kovalchuk got the puck past Fukufuji.
"He's making history here," Hossa said of the 24-year-old goalie.
Barry Brust went the rest of the way in nets, turning aside 17 of 20 shots but letting it get out of hand in the closing minutes. The Thrashers scored three times in the last 6:56 against the Kings, who have surrendered an NHL-worst 176 goals.
"That's just the way it's been going," forward Craig Conroy said. "We give up a lot of goals ... and there's nothing we can do about it. We just have to try to get better defensively and help our goaltenders. They've been under a lot of pressure."
Los Angeles had a chance after Kostopoulos knocked in a rebound on Lehtonen, who was flat on his stomach in the net after being inadvertently tripped by teammate Vitaly Vishnevski.
But Hossa ended any hopes of a comeback, scoring on a nifty power play after working the give-and-go with teammate Slava Kozlov. Hossa was alone in front and shifted to his backhand to beat Brust.
Metropolit swept a loose puck into the net, then Hossa brought out the hats when he scored on a breakaway with a less than two minutes remaining.
Despite his rough outing, Fukufuji said he hopes to be an inspiration to other Japanese players.
"It's my dream," he said. "I've watched on TV since I was 9 or 10 years old. I'm here now."
- Hossa has 21 points (seven goals, 14 assists) in his last 14 games.
- Hossa also had a hat trick Nov. 30 against Toronto and has six three-goal games in his career.
- The Kings are without starting G Dan Cloutier, who underwent hip surgery last week, and backup Mathieu Garon, who is on the injured list because of a finger problem.