There wasn't anything much more sure than Serena Williams at least playing for a chance at history in the women's final of the US Open on Saturday afternoon.
At least, that's what those who bought tickets to the match thought as prices soared for the chance to witness the first single-season Grand Slam since Steffi Graf did it in 1988.
And then the unthinkable happened, and Williams lost in three sets to Roberta Vinci in Friday's semifinal. Ticket prices plummeted.
Before the match started, the average list price on the resale market was $1,412, with a get-in price of $271, according to a resale market tracking firm.
Immediately after the match, at 2:58 p.m. ET, the average list price fell to $1,103, with the get-in price dropping to $124.
By 3:07 p.m. ET, as the world began to digest that the US Open would feature an all-Italian final between Flavia Pennetta, seeded 26th, and unseeded Vinci, prices continued to drop. The average list price had fallen to $876 and the cheapest ticket was down to $70, according to TiqIQ data.
And prices didn't stop falling. By 3:20 p.m. ET, just 20 minutes after the match, the average list resale price was down to $680 and the get-in was $40, discounts of 50 percent and 85 percent, respectively, from the prices before the match.
Thanks to the hype of Serena's potential feat, this year marked the first US Open when the women's final sold out before the men's final.