Hari knocked Saki down three times in the first en route to the win, with the first coming on an uppercut. He battered him throughout the rest of the round in scoring the stoppage for the 64th knockout of his carer. His career record now stands at 78-11.
The 27-year-old will now turn his attention to the heavyweight boxing scene.
The 6-foot-5, 240-pound Hari has long been considered one of the top kickboxers in the world, having won the K-1 world heavyweight championship twice.
Saki fell to 75-15 with the loss.
In other action during the event, longtime MMA fighter Melvin Manhoef lost a decision to Tyrone Spong. Spong is one of UFC light-heavyweight contender Rashad Evans' striking coaches.
Hafid el Boustati def. Henri van Opstal via unanimous decision
Andy Ristie def. Hinata Watanabe via KO, Round 1
Sahak Parparyan def. Mourad Bouzidi via majority decision (4-1).
Ben Edwards def. Ricardo van den Bos via unanimous decision.
L'houcine "Aussie" Ouzgni def. Yohan Lidon via unanimous decision.
Tyrone Spong def. Melvin Manhoef via unanimous decision.
Anderson "Braddock" Silva def. Michael Duut via unanimous decision.
Harut Grigorian def. Chris Ngimbi via TKO (cut) in Rd. 2.
Errol Zimmerman def. Rico Verhoeven via KO, Round 1.
Robin van Roosmalen def. Murat Direkci via majority decision (4-1).
Daniel Ghita def. Hesdy Gerges via KO, Rd. 1
Badr Hari def. Gokhan Saki via KO, Rd. 1