PA PhotosJenny Gunn rescued the hosts from a tricky situation as her unbeaten 36, from 46 balls, guided England past India's 173 for nine with just six balls to spare.
England had slipped to 105 for five in pursuit as Nagarajan Niranjana (three for 24) claimed the key wicket of Sarah Taylor (43) leg before.
But Gunn, who earlier took one for 20, took over hitting four boundaries as she got just enough support from the tail to ensure a series decider in Wormsley on Wednesday.
India, who had led the series 2-0, had earlier posted a challenging total following half-centuries from Mithali Raj (58) and Harmanpreet Kaur (55), while Arran Brindle grabbed three for 20.
