The Staten Island Zoo's 34 year-old prognosticating spider monkey is now 4-0 after Stanislas Wawrinka's five-set 7-6 6-7 7-5 4-6 6-4 thriller victory over American Sam Querrey at the US Open.
Every morning, after eating, Grandpa picks from two tennis balls in his exhibit, each one labeled with a player competing in a match chosen at random.
Whichever ball Grandpa grabs first is his call for the winner. So far, he has correctly predicted wins by Alona Bondarenko, Mardy Fish, Elena Dementieva, and Wawrinka.
On Monday, Grandpa's tail accidentally brushed first against Querrey's ball, most likely an omen that it would be a close match, before he grabbed and bit down forcefully on Wawrinka's ball.
Tuesday morning, when given the choice between Estonia's Kaia Kanepi and Russia's Vera Zvonareva, Grandpa went for the upset.
After eating his breakfast of grapes and rice cakes, and tearing down maple branches set up in the back of the exhibit, Grandpa swung over to the balls, and quickly snatched up Kanepi's, going so far as to ignore Zvonareva's ball for the next few hours.
Kanepi, who is seeded 31st, is considered a major underdog to the Zvonareva, seeded seventh.