Gamba Osaka completed Japan's domestic treble on Saturday by beating Montedio Yamagata 3-1 in the Emperor's Cup final, celebrating wildly as a shower of confetti rained down.

Striker Takashi Usami scored twice in Yokohama to fire a timely reminder to watching Japan coach Javier Aguirre, who has bizarrely overlooked the sharp-shooting former Bayern Munich striker since taking charge of the Blue Samurai after the World Cup.

The Mexican is set to name his Japan squad for next month's Asian Cup on Monday, and Japan's hopes of retaining their crown would clearly be boosted with Usami's inclusion.

Gamba, who wrapped up their second J-League title last weekend to cap a sensational return to the top flight following a chastening year in division two, became only the second side to achieve the Japanese treble since the J-League was launched in 1993, Kashima Antlers having done it in 2000.

"I'm very proud of the players," Gamba manager Kenta Hasegawa told NHK Television. "The team has shown fantastic togetherness. We've stuck to our style of playing all year and this is an amazing way to finish and amazing season."

Gamba, also this year's J-League Cup winners, lifted the Emperor's Cup -- Japan's version of the English FA Cup -- for the third time after winning it in 2008 and 2009.

Usami struck with a superb goal after just four minutes in Saturday's final, reacting with lightning speed to prod home the loose ball after his initial volley had been well stopped by goalkeeper Norihiro Yamagishi.

He turned provider in the 22nd minute, setting up Brazilian strike partner Patric, who curled a shot into the top corner as Gamba went in at the break leading 2-0 in front of 47,000 at Nissan Stadium.

Romero Frank pulled one back for Yamagata, who have secured promotion from the second division this season, but Usami blasted home his second from the edge of the box with five minutes left to seal the victory.

Usami said: "It's something I'll never forget. We wanted to finish the season in style -- it's a dream come true."

Gamba's fairytale season is all the more remarkable as the former Asian champions had been languishing near the foot of the table before the World cup break but won 15 of their last 20 matches to win the J-League for the first time since 2005.

"In the 20-odd years since the J-League began only Kashima had done the treble so it's a real honour," said Gamba captain Yasuhito Endo, Japan's most capped player and this season's J-League player of the year. "It's all been down to hard work and team spirit."