After ripping 21 hits and five home runs in a double header sweep on Saturday, the Panthers (11-10 overall, 2-1 Missouri Valley Conference) were held to just three hits.
The Sycamores won it on a bases-loaded, single by Shaye Barton in the bottom of the eight.
ISU took a 1-0 lead in the second with a solo home run by Brooke Mann. UNI tied it as Adara Opiola hit her second home run in as many days in the top of the fourth.
The Sycamores (10-12, 1-2) loaded the bases against UNI relievers Eric Oler and Brooke Craig in the eighth on a single and a pair of walks, second walk intentional.