Robinho, who had last played at Vila Belmiro in August 2005 before his transfer to Real Madrid, scored Santos' second goal when he touched home from Neymar's free-kick just before the half hour.
He scored again 13 minutes into the second half with a deft lob over the goalkeeper to make it 5-1 and ran to celebrate with his two-year-old son, as Santos went four points clear at the top of the Paulista (Sao Paulo) state championship.
Robinho has scored three goals in three matches, all victories, since his return on a six-month loan last month.
Struggling Palmeiras sacked coach Muricy Ramalho after Wednesday's 4-1 home defeat by Sao Caetano.
Ramalho, who steered Sao Paulo to three successive Brazilian championship titles from 2006 to 2008, became the fourth coach to lose his job in Brazil's top flight this year.
Having taken charge in July, Ramalho lasted less than seven months at Palmeiras after failing to steer them into this year's Libertadores Cup, the top South American club competition they won in 1999.
Palmeiras appointed former AS Roma and Brazil defender Antonio Carlos Zago, who had been in charge of Sao Caetano, as Ramalho's replacement. He takes over with Palmeiras in eighth place in the Paulista standings.
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