Australia's Thanasi Kokkinakis has again been caught up in controversy, with the tennis youngster involved in an on-court altercation with American Ryan Harrison at the Cincinnati Masters.

Tensions between the 19-year-old Australian and 23-year-old American bubbled over during the match, won by Kokkinakis 7-5 3-6 7-6 (7-2).

Kokkinakis was met with threats of violence by the American pro in a heated on-court clash.