On April 25, 2014, Istrate challenged Jérôme Le Banner for his ISKA K-1 World Super heavyweight title.
[1] On October 24, 2015, Istrate participated in the Venum Victory World Series 95 kg elimination tournament in Panama.
He defeated Lucas Alsina by unanimous decision in the semifinals and Rafael Da Souza by technical knockout in the third round to earn a place in the main VVWS tournament.
[4] Istrate faced Bas Vorstenbosch in the quarterfinals round of the 2016 A1 World Combat Cup on November 5, 2016.
[5] Istrate faced Costin Mincu in the opening round of the 2019 Tatneft Cup +80 kg tournament, held on June 11, 2019.
[8] On February 25, 2023, Istrate faced Niknam Haghparast at Mix Fight Events 52 as the quarterfinal of a Road to ONE tournament.
Istrate was up on points as he had scored a knockdown before the stoppage and was therefore picked as the qualified fighter for the upcoming K-1 World Grand Prix 2024 Final.