Seoul edged to only their third league success of the season in the final game before the K-League takes a near seven-week break.
And it was Park who struck with his first goal of the campaign four minutes from time to secure triumph for the hosts, who moved level on points with Seongnam as a result.
The result extends Seongnam's 11-year league winless run away from home against Seoul, and keeps them seven points adrift of the top six.
Seongnam stay eighth in the table despite the defeat, while Seoul are up to ninth with only goal difference separating the two teams.
The K-League will resume on July 5.
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