Serena Williams
Serena Williams (pictured) returns a shot to her sister, Venus Williams, during their quarterfinal match at the U.S. Open tennis tournament in New York Sept. 8, 2015. Reuters

With Serena Williams just two U.S. Open wins away from completing the first calendar-year grand slam in women's singles play in nearly three decades, the secondary ticket market is clamoring for the opportunity to catch a glimpse of history. But vendors need Williams to secure a berth in the championship match to keep fan interest at its current rabid level.

Williams defeated her sister, Venus, in three sets Tuesday to advance to Thursday's semifinals, where she'll face Roberta Vinci, a 32-year-old Italian playing in her first major. After wins at this year's Australian Open, French Open and Wimbledon, Serena Williams, 33, needs to win this U.S. Open to achieve the first calendar-year grand slam since Steffi Graf accomplished the feat in 1988. Williams is the heavy favorite, having won the U.S. Open the last three years and reached the final in the last four.

The historic run has pushed ticket prices on the secondary market to monstrous levels. The average ticket price for this year's women's singles final stood at $1,442.21 as of Wednesday morning, according to Chris Matcovich, director of data and operations at TiqIQ, a ticket aggregator. That's more than five times as expensive as the average ticket price in 2010, which sank to $280.50 on the secondary market after Williams withdrew due to an injured right foot.

Williams' presence in the U.S. Open final has had a demonstrable effect on secondary market ticket prices. Average prices jumped to $383.46 in 2011 for the final between Williams and Samantha Stosur (which Stosur won), according to TiqIQ data.

The possibility of a calendar-year grand slam has "definitely played a part" in this year's exorbitant prices on the secondary market, Matcovich said. In addition, this year's U.S. Open is spread across 24 sessions, as opposed to 26 sessions last year. With less of an opportunity to view matches, fans are paying a premium.

Average ticket prices are up across the board at this year's U.S. Open, held, as always, at Arthur Ashe Stadium in Flushing, New York. The average secondary market price held at $378.22 last month, up 25 percent from last year, Forbes reported. U.S. Open ticket prices are the highest they've been since at least 2010, when TiqIQ started tracking the numbers.

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