The 35-year-old penalty corner exponent rolled back the years after Japan, regarded along with India as Pakistan's toughest opponents in group B, took the lead in the third minute.
Kenji Kitazato's early goal was equalised the very next minute by Fareed Ahmed before Abbas converted his first goal in the 20th minute and Muhammad Rizwan made it 3-1 before half-time.
Pakistan pumped in five goals in relentless raids on the Japanese defence in the second-half that began with a second goal from Abbas in the 51st minute.
Muhammad Imran netted a penalty stroke, while Muhammad Waqas, Shakeel Abbasi and Muhammad Zubair completed the emphatic win ahead of Saturday's crucial game against India.
Pakistan are hoping to bounce back in Guangzhou after a lean year in which they finished last at the World Cup and an embarrassing sixth at the Commonwealth Games.
The Pakistanis, who won the last of their seven Asian Games gold medals in Beijing in 1990, have not bagged a major title since the World Cup triumph in Sydney in 1994.
"This was an important win because we knew that beating Japan was important if we were to make the semi-finals," said Pakistan's star striker Rehan Butt.
"The margin of victory suggests we were in control of the game despite the early goal by Japan. We have settled down well."
Pakistan had thrashed Hong Kong 12-0 in their first match.
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