Match reporter: JOHN LAING
The Swifts came from behind to collect all three points at a sunny Memorial Park.
It was Murray Black who put the Hibs ahead in the 31st minute with a well-taken effort from a tight angle then Ross Hain had a shot saved by Reece Beveridge to prevent Craig Gilbert's side from doubling their advantage.
The visitors came close to equalising in the 44th minute when Grant Hamilton headed Dylan Vannett's corner-kick just wide.
The second-half had just started when Vannett headed wide when it looked easier to score but the former Hibs man, Mitchell Sharp, enjoyed better fortune in the 51st minute to level affairs.
Within the space of just a few minutes Beveridge pulled off two 'Alisson Becker' type saves from Andy Adam and then to rub salt in the wounds, Sharp at the other end punished slack defending to complete the scoring in the 80th minute.
This was Thornton's third league defeat on the trot so they'll be anxious not to make it four when they travel to take on Heriot-Watt Uni next Saturday.
Thornton Hibs: Doctor, Rodger, McMillan, Allan, Cunningham, Adam, Black, Hain, Keatings, Thomson, Westwaters. Subs: Soutar, McNab, Jolicoeur, Jefferies.
Inverkeithing HS: Beveridge, Paterson, Hall, Tottman, Hamilton, Holness, Sharp, White, Allan, Thompson, Vannett. Subs: Goodall, Robertson, Mansouri, Reid, Wishart, Ramage.
Referee: Mr C.Sanderson
Attendance: 120