The Ugly Betty star joined actor Kelsey Grammer and rap superstar Jay-Z at the Audemars Piguet Time to Give event, where a selection of celebrity-designed watches, autographed by the stars themselves, went under the hammer.
Jay-Z managed to bump up sales of a timepiece created and signed by former Frasier star Grammer by stepping on stage to take offers for the prize, while his own design sold for $220,000 (£146,700), reports the New York Post.
But Williams took the auction one step further by adding a musical element to the sale when bids on another watch rose to $132,000 (£88,000).
A source tells the New York Daily News, "Vanessa promised that if people bid enough, she would perform. Sure enough, after someone shelled out $132,000, she sang a song from (her Broadway show) Sondheim on Sondheim."
The event was held in support of Broadway Cares/Equity Fights AIDS, a charity supporting individuals affected by HIV/AIDS.