After a scoreless first half, Socceroos striker Cahill struck early in the second period.
Shanghai front man Demba Ba brought down a cross in the box and Cahill was first to react to the loose ball, before thundering home the opener.
► When the ball drops in the area, who else would you want there but Tim Cahill? Another goal for Shanghai Shenhua by the Socceroos legend. Posted by SBS The World Game on Monday, 27 July 2015
It was the 35 year-old's seventh goal of the campaign and his sixth in seven matches for the club.
It proved enough to secure the home side all three points which moves it into fifth place in the Chinese Super League.