Korea captain Koo Jacheol doubled their lead from 15 yards on 57 minutes.
Japan skipper Maya Yoshida saw his late header disallowed for a foul on Korean keeper Jung Sungryong.
Korea, convincingly beaten by tournament favourites Brazil in the last four, had never previously progressed past the Olympics quarter-finals and their victory in the Millennium Stadium was greeted by joyous celebrations at the final whistle.
“Japan didn’t create anything. They were outmuscled in the early part of the game and you thought their technical ability would come through in the second half, but it didn’t. Korea were very stubborn, scored goals and asked questions. Japan had no answer.
“Korea celebrated like they had won a gold medal – and they thoroughly deserved it on the day.”
Japan had not conceded a goal in the tournament before their 3-1 semi-final defeat by Mexico, but their defensive frailties were exposed for the second successive game as Korea capitalised.
An isolated Park latched on to a long ball before superbly twisting and turning into space to fire a low shot past Japan goalkeeper Shuichi Gonda at his near post.
Japan pushed and probed in search of an equaliser, but they were hit by a sucker punch when a huge punt by Korea goalkeeper Jung Sungryong found Koo who lashed into the bottom corner.
The rivalry between the two nations threatened to boil over shortly after the half-hour when Koo became the third Korean player, after Ki Sungyueng and Oh Jaesuk, to be booked for cynically fouling Japan’s Yuki Otsu.
The Japanese players were furious with the rough treatment received by Otsu, who appeared to have been identified by Korea as the dangerman following a series of impressive Olympic displays.
But Otsu could not inspire a Japan comeback as their tearful players slumped to the turf in despair at the final whistle.