The U.S. claimed a third win in Milan by beating Switzerland 5-0 and Germany snatched a 2-1 overtime victory against France.
Sweden top Group B on nine points, with Italy three points behind in second. Germany are third with five, Japan have three and France are on one having completed all four matches.
Italy and Germany meet on Tuesday, with Japan facing Sweden in the group's concluding games. The top three advance to the last eight.
Italy's Matilde Fantin scored twice in the opening period before Japan's Rui Ukita reduced the deficit in the second. Kristin della Rovere netted the Italians' third goal early in the final period but Akane Shiga's goal set up a nervy ending.
Italy had gone in front when Laura Lobis played the puck off the boards and Fantin collected it to send a wrist shot into the roof of the net. Fantin netted again on a power play but Japan then pulled one back through Ukita's one-timer.
Italy pulled off some desperate defending late in the second period as Japan began to rack up the shot count.
The players had been back on the ice mere seconds when Della Rovere intercepted the puck and, after her first shot was saved, she netted the rebound to restore Italy's two-goal advantage.
Shiga's goal was awarded after a video check with nine minutes remaining but Italy survived a late onslaught at Milano Rho arena.
Canada win overshadowed
Canada had little trouble earning a second win with a 5-1 thrashing of Czech Republic, but Poulin played no part after the opening period where she took a heavy hit into the boards.
The Czechs had a two-player advantage early on but the Canadians resisted and Renata Fast was barely back on the ice from the penalty box when her shot was saved and Kristin O'Neill tapped in the rebound.
The Czechs killed a penalty for Kristyna Kaltounkova's illegal hit on Poulin but the Canada doubled their lead with the sides back to equal strength, Sarah Fillier reaching back to send her rebound shot into the roof of the net.
Less than 40 seconds later Laura Stacey collected Emma Maltais' long pass and sent her shot sailing past Julie Pejsova and the Czechs immediately replaced their goaltender with Michaela Hesova.
Before an action-packed opening period ended, it was the Czechs' turn to play three against five, Kaltounkova again one of the culprits, and the Canadians needed just half a minute for Julia Gosling to net their fourth.
Canada were in no mood to let up, Gosling scoring again 17 seconds into the second period with her side still on the power play. There was no further scoring until Natalie Mlynkova's consolation power play goal midway through the final period.
US thrash Switzerland
The United States continued their unbeaten streak at Santagiulia by cruising past Switzerland.
Defender Haley Winn opened the scoring six minutes in from a perfect assist from Caroline Harvey and the U.S. got a bit of luck late in the second period when forward Joy Dunne's shot bounced off the skate of Swiss defender Stefanie Wetli into the net.
Forward Hannah Bilka added another score with a tip-in from the side of the crease less than two minutes into the third period, while Alex Carpenter and defender Harvey added two more goals in rapid succession.
Switzerland play Finland in their final Group A game, while the U.S. face Canada in what is widely expected to be a preview of the gold-medal game, both on Tuesday.
All five teams from Group A will advance, with their seeding in the last eight depending on placings in the preliminary standings.
Germany outshot France 46-14 in normal time but after taking an opening-period lead they were stung by Estelle Duvin's final-period goal. Katarina Jobst-Smith netted the winner after just over one minute of overtime.
The Germans made their fourth power play count when Laura Kluge netted in the final minute of a first period where France managed a mere two shots.
France withstood further pressure to keep Germany scoreless in the second period and out of nowhere Duvin equalised before the midway point of the final period.
The Welcke twin sisters, Luisa and Lilli, provided the assists for Jobst-Smith's winning strike.