Organizers cite a technicality in the WTA’s structure to justify the pay differential. The tournament is one of nine Masters 1000 events, the top tier on the ATP Tour. But the top tier of the WTA Tour is four Premier Mandatory events, which include tournaments in Miami, Madrid and Indian Wells, where women can expect equal compensation to men. The Ohio event sits in the next tier, the Premier 5.

Women are also paid less than men at similar Premier 5 events in Canada and Rome, which are held in conjunction with men’s tournaments. (At all tour events outside the Grand Slams, men and women play best-of-three-set matches.)

Many WTA-only events, including the one now known as the Volvo Car Open, have flourished. Attendance here consistently dwarfs lower-tier ATP events nearby in Atlanta and Winston-Salem, N.C., and it has drawn crowds similar to, or ahead of, the ones at the comparable ATP event in Washington, which added a lower-tier WTA field in 2012. But the total men’s purse in Washington is $1,877,705, while the Charleston purse was about $753,000.

“There’s no question that we want to lessen that gap — it’s our commitment to the players,” said Bob Moran, the Volvo Car Open’s tournament director.

There are occasional combined events at which a higher-tier WTA event pays a larger purse than its lower-tier ATP counterpart. At the China Open, held in Beijing in October, the men’s champion earns 67 percent of the pay earned by the women’s champion. But the disparity is steeper at tournaments in which the ATP event is of a higher designation. In Rio de Janeiro in February, the men’s champion, Pablo Cuevas, won $303,300, more than seven times the $43,000 paid to the women’s champion, Francesca Schiavone.

The pay gap extends all the way down the ladder on the ATP and WTA tours. According to a 2014 study by the International Tennis Federation that analyzed the average costs for playing professional tennis and the prize money from the previous year, 336 male players could earn enough to cover average expenses, while only 253 women could.