Repeatedly leaving the Japanese defenders stunned with his drag-flicks, Rupinder converted his first four penalty corner shots as fancied India steam-rolled over the hapless Japanese defence.
Left playing a supporting role to Rupinder, striker Ramandeep Singh scored twice in the first quarter, while Talwinder Singh and Yousuf Affan contributed one goal each.
Japan’s goals, against the run of play, came through Kenta Tanaka and Hiromasa Ochiai.
With Rupinder converting six of India’s 10 penalty corners, it was a day to forget for Japan, who won the silver medal in the last Asian Champions Trophy behind Pakistan in 2013.
Ramandeep opened the India account in the second minute after picking up a pass from Sardar Singh and shot past Japanese goalkeeper Mashahito Kunitomo.
Rupinder then got into the goal-scoring act in the seventh minute with a stinging drag-flick into the right corner on India’s first penalty corner. Three minutes later, he sent a rising drag-flick into the net for his second goal.
Ramandeep’s reverse drive from top of the circle in the 15th minute caught the Japanese custodian on the wrong foot and sounded the boards to give India a 4-0 lead in the first quarter.
Rupinder’s low flick went into the citadel off the goalkeeper’s pads in the 17th minute before Talwinder Singh slotted a reverse hit past the goalkeeper in the 19th minute.
Rupinder converted his fourth successive penalty corner shot in the 22nd minute to boost India’s lead to 7-0, before Japan benefitted from a lapse in the Indian defence in the next minute that paved the way for Kenta Tanaka to score with a flash strike.
Hiromasa Ochiai defelected in a cross from right in a crowded circle for Japan’s second goal in the 38th minute.
Rupinder sent a rising shot into the roof of the cage in the 46th minute and got his sixth goal a minute later with a grounder that trickled into the goal off a defender’s stick.
Yousuf rounded off India’s scoring in the 50th minute with a flash strike in a crowded zone and the goal was confirmed after a video referral.
Earlier, hosts Malaysia stunned twice defending champions Pakistan 4-2 with Faizal Saari scoring two goals in the home team’s rally from 1-2 deficit.