Sisson ran the Chicago Marathon in 2:18:29, finishing second in the race.
This was faster than the previous record of 2:19:12, set by Keira D'Amato on January 16 in Houston.
"The women standing here today have achieved a lot, so it's an incredible honor to be among them," Sisson said.
Kastor, who held the record before D'Amato, called Sisson's race "incredible".
D'Amato, who was overseeing Sisson's run as an analyst for NBC Chicago, said he was "really proud" of Sisson.
Kenyan runners Benson Kipruto and Ruth Chepangetich won the Bank of America Chicago Marathon.
Emily came second, John Korir took third place.