This was India's biggest win since their 7-4 triumph against Pakistan in the 2010 Commonwealth Games at New Delhi.
Playing their best game of the tournament, Manpreet Singh opened the scoring for India in the fourth minute but Pakistan equalised in the seventh through captain Muhammad Irfan.
But thereafter it was all India as the Sardar Singh-led side controlled the proceedings with SV Sunil scoring two opportunistic field goals in the 10th and 41st minutes.
India's victory would have been bigger had Rupinder converted a penalty stroke in the 55th minute and an deflection into the net by Ramandeep Singh in the 69th was not disallowed after the umpire initially blew for a goal.
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The victory took India to the second spot in the round-robin league standings with nine points from four outings. The table is being led by world champions Australia on 12 points from four straight wins.
The all-important goals for Australia was scored by captain Jamie Dwyer, who capitalised on a rebound to shoot into the open goal with the goalkeeper at his mercy.
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India got off to a flying start with Manpreet picking up a short pass from Sunil on the left and shooting on target with a firm reverse drive in the fourth minute of play.
Pakistan equalised within three minutes when they forced two successive penalty corners with captain Muhammad Irfan converting the second one with a low drag-flick to the right of Indian goalkeeper Akash Chikte.
Pakistan goalkeeper Imran Butt then brought off a fine save when he leapt to his left to palm away a rasping drag-flick by Rupinder from India's first penalty former in the 18th minute of play.
Rupinder was off the field, serving two minutes for a green card suspension, when Pakistan earned their third penalty corner, but Irfan's rising drag-flick struck Manpreet on the knee and he had to limp off the pitch.
Sunil boosted India's lead to 3-1 when he pushed the ball into an open goal after receiving Nikkin Thimmaiah's square pass on an opening created by Kothajit Singh's push from the sideline in the 41st minute.
Manpreet later came back to earn India a penalty stroke, when he was tripped in the scoring zone, but Rupinder sent the flick straight into the goalkeeper's pads.
India will next play title holders New Zealand tomorrow.