A dramatic match complete with 679 runs ended on Wednesday with the diminutive 21-year-old Illingworth remaining calm and collected with Australia on 8-322, still needing 17 off nine balls to drag her side home past the hosts' formidable 6-338.
This tall order proved no problem for Illingworth, who hit the last two balls of the penultimate over for six, before striking the winning boundary in the final over to square leg with three balls remaining to keep Australia in the series.
With the visitors having lost the first match by four wickets, Illingworth's match-winning 22 off 14 balls ensures there's everything to play for in Friday's series-decider, also in Mohali.
Illingworth also took 2-44 off her five overs, dismissing India's two openers as the hosts, having decided to bat first, set up a substantial target, largely off the back of captain Yastika Bhatia's 112 from 84 balls.
Illingworth's pace partner Darcie Brown was the Australian standout with the ball, taking 3-39 off her eight overs, including three wickets in her last three overs.
Captain Tahlia Wilson led Australia's response from the front with her 77 off 79 balls, but the real impetus came from No.3 Anika Learoyd, who smashed 54 from 29 balls, with nine fours and two sixes, and Charli Knott, who made 63 off 37, with three sixes and seven fours.
Minnu Mani took three wickets, getting rid of both Wilson and Knott, as Australia began to slip but the chase was regenerated by Tess Flintoff's 38 from 43 and Hayley Silver-Holmes, who scored 47 from 51 before Illingworth's decisive late cameo.
