Rachel Alexandra is taking on a new challenge: racing against older horses in a bid to become the first filly to win the Woodward Stakes.

After dominating the 3-year-old filly division with romps in the Kentucky Oaks and the Mother Goose, and beating the 3-year-old boys in the Preakness and the Haskell Invitational, Rachel Alexandra will run against older competition for the first time in the Sept. 5 race at Saratoga Race Course.

The decision was announced Monday by trainer Steve Asmussen following workouts by the filly and 3-year-old colt Kensei, both owned by Jess Jackson.

Asmussen said Kensei will run in Saturday's Travers Stakes, a race for 3-year-olds. The Woodward is for horses 3 years and older.

Rachel Alexander covered six furlongs in 1:12.58 while under stout restraint on Monday. Kensei, winner of the Jim Dandy Stakes in his most recent start, worked a half-mile in 50 seconds.

"Rachel Alexandra's workouts have been excellent," Jackson said in a statement. "Hal McCormick (the minority partner), my family and I, like other fans of horse racing, want to see her tested. If she goes up against older male horses, we'll be better able to get a measure of her greatness."

Shortly after the announcement, the New York Racing Association said it had raised the purse for the 1 1/8th mile Woodward from $500,000 to $750,000.

"Raising the Woodward purse will help attract a top field to what will be a historic race," said P.J. Campo, NYRA vice president and director of racing. "In addition, we felt that to have a filly like Rachel Alexandra seeking to become the first ever female to win the Woodward warranted an increase in purse."

The filly has won eight races in a row and is the leading contender for Horse of the Year.