However, Japan, who suffered in all five matches during their campaign of Hockey World League semifinal round, were rendered helpless against India - the world's sixth-ranked side, who controlled the game nicely and scored one after another goal to leave the field with their heads held high.
India earned a penalty corner in the 21st minute but failed to convert it into a goal.
All Captains of the participating teams pose with the Asia Cup Trophy. India and Japan were level 1-1 after the end of first quarter.
India netted through Sunil Sowmarpet (third), Lalit Upadhyay (22nd), Ramandeep Singh (33rd), Harmanpreet Singh (35th, 48th). Japan pulled one back the next minute with Kenji Kitazato leveling the scores.
Preview: Eyes firmly set on retaining the numero uno status in the continent, favourites India face a tricky campaign-opener against Japan in the men's Asia Cup hockey tournament starting on Wednesday. Harmanpreet scored his second goal to make it 5-1 in India's favour.
"The first match is always hard as the players need time to settle down".
Hero Asia Cup 2017 is one of the premier hockey tournaments globally and is a much sought-after competition that promises great entertainment.
On the opening day, all the four teams of pool A will be in action. It was also a winning debut for Sjoerd Marijne as National Coach.
The teams went into half-time with India leading 2-1.
This sensational win against Japan must have issued a warning to other Pool A participants - Bangladesh and Pakistan - who will be facing India next.