The 'Mrs Doubtfire' star, who died of an apparent suicide at his home in Paradise Cay, California in August, was a loyal Giants fan, reported Contactmusic.
His three children attended the team's final home game of the championship at At&T Park, but it was Zak who took to the mound for the ceremonial throw to his dad's longtime friend Crystal, another devoted baseball fan.
As part of a pre-game tribute, clips of Williams at Giants games were shown on the Jumbotron big screen. The three kids were each gifted team jerseys with 'Williams' on the back.
"We could not think of a better way to celebrate his memory," the trio said in a statement.
Actors Rob Lowe and Benjamin Bratt were among the other celebrities at the ballpark, while rocker Aaron Lewis performed the US National Anthem before the game, which the Giants won 5-0 to take a 3-2 lead in the World Series.