The pent-up fraustration of Japanese champions Sanfrecce Hiroshima exploded Sunday when they smashed Omiya Ardija 5-1 away for their first win of the J-League season.

Japan under-23 striker Takuma Asano was among the scorers in a dominant display in Saitama but it came at a price. The player suffered a heel injury and is set to miss the Olympic squad's trip to Portugal this week.

Hiroshima's victory at the home of the Squirrels was a first in four first-stage matches. It leaves them five points adrift of leaders Kawasaki Frontale, who improved to 10 points after thumping Ventforet Kofu 4-0 away on Saturday.

Promoted Omiya began the campaign with back-to-back wins but normal service appears to have resumed since then for a club used to yo-yoing between the top two divisions.

Hiroshima will also be hoping Sunday's result brings some stability after a shaky start to their J-League title defence and a pair of Asian Champions League setbacks.

They banished some of their ACL demons by putting Thailand's Buriram United to the sword with a 3-0 midweek win, before carrying on where they left off against an Omiya side which showed little stomach for a fight.

"We hadn't won yet in the J-League and we are a little way behind the leaders but this will give the players confidence," Hiroshima manager Hajime Moriyasu told local media.

"If we can keep doing what we are doing now, the results will come."

In Sunday's other J-League game, Urawa Reds won 2-0 at Shonan Bellmare thanks to goals either side of the break from Tadanari Lee and Shinzo Koroki.

That win took Japan's best-supported side second on nine points, ahead of Kashima Antlers by virtue of superior goal difference. Once-mighty Kashima beat Tokyo 2-0 at home on Saturday.