Akane Shiga, Rui Ukita, Haruna Yoneyama, and Hanae Kubo scored for Japan. Haruka Toko sparkled with two assists.
"We had the hardest time in the last game against the Czechs," said Ukita, who got the deciding goal in the second period on the power play. "Today's goals brought a feeling of confidence."
Captain Fanni Gasparics replied for the newly promoted Hungarians, who remain winless in three tries. Hungary is eliminated from quarter-finals contention.
"Right now, we're pretty disappointed," said Hungary's Mira Seregely. "This was a game we thought we could win and we wanted to win. I think that everybody can see that, that we played really good, especially in the beginning. We can only move on and prepare for the next game."
It was a true battle of power plays as Japan capitalized three times and Hungary once. The Japanese bounced back in style after getting shut out 4-0 by the Czech Republic in their last game. They outshot Hungary 29-25.
Japanese coach Yuji Iizuka was happy to earn another win in light of the challenging run-up to these Women's Worlds: "It's been a hard time the last two and a half years. We've had almost no opportunities to play the game on the international stage."
In goal, two-time Japanese Olympian Nana Fujimoto got her third consecutive start. Aniko Nemeth played her second game after making 23 saves in Hungary’s 3-0 opening loss to Germany.
The Hungarians put more pressure on Fujimoto’s net in the early going, but Nemeth had to be sharp as well to get her blocker on Aoi Shiga’s drive through traffic.
With under five minutes to play in the first, Akane Shiga – Aoi’s younger sister – pounced on Hungarian blueliner Lotti Odnoga’s defensive-zone giveaway and forced Nemeth to make her best save of the stanza with a glove grab.
Hungarian coach Lisa Haley praised Nemeth: "She's by far our most-improved player from the day I started a year ago. She's in phenomenal shape. She really wants it. She's proven again today that she can be relied upon."
The Japanese had another fabulous chance on a 3-on-1 rush that fizzled and hit the cross bar. At 19:18, Hungary’s Petra Szamosfalvi was sent off for hooking, and Akane Shiga banged in a power-play rebound to open the scoring just 17 seconds later as the Japanese swarmed the net.
At 3:16 of the second period, Hungary struck back on an early power play. Japan’s Chika Otaki was sent off after dumping Odnoga into the boards on the forecheck. Gasparics took a pass from Sarah Knee, waltzed into the left faceoff circle, and fired the puck high past Fujimoto on the short side.
A 5-on-3 power play enabled Japan to retake the lead at 7:30, as Haruka Toko found Rui Ukita in the low slot and she confidently roofed it home.
"Japan has a ton of structure, and that also includes their power play," said Haley. "They know exactly where they're going next. And for us, I think one of the adjustments in zone is definitely trying to dictate where the next pass goes, instead of reacting to where they're gonna put it. We were always a half a second behind that way. And obviously, we're relying on our goalie to have to make some second and third saves."
The Hungarians fell short with two more power play opportunities to close out the middle frame and another two in the first half of the third period.
Nearing the seven-minute mark of the third, Nemeth gave her team a chance when she stoned Suzuka Taka on a clearcut breakaway, denying the five-hole attempt.
Akane Hosoyamada's power-play howitzer was deflected in by Yoneyama for a 3-1 lead at 10:23.
"I think they have a good team," said Hungary's Emma Kreisz. "We have one too, but they are a little bit faster. They think faster. And I think that made the difference between the two teams [tonight]."
After Mei Miura centered the puck from a nice right-wing rush, Hanae Kubo, Japan's 38-year-old national team legend, poked it in at the side of the net at 11:34 to make it 4-1. It was her first goal and point here in Calgary. That killed Hungary's comeback hopes.
"In this game I had very limited time to play," said Kubo, who logged just 1:57 in the third period and 7:48 on the night. " But I scored a goal, so I'm very excited that I helped us to win."
Japan also topped Hungary 4-2 in a pre-tournament exhibition game on 18 August on the strength of two goals by Rui Ukita.
Hungary closes out its round-robin slate versus fellow top-division newcomer Denmark on Wednesday. Japan does the same versus Germany on Thursday.
"It would have meant a lot to win today's game," Haley said. "Yes, this World Championship is a free pass in terms of teams not getting relegated. But I'm trying to help my team get as much experience as possible. Winning today would really have set us up to feel what that kind of pressure would be like next year, to have to win to try to get into a quarterfinal."