Alistair Cragg broke Mark Carroll's 13-year-old Irish 5,000 metres record at Friday's Diamond League meeting in Brussels.
US-based Cragg clocked 13.03.53 when finishing fifth in a world class field - almost four seconds faster than his previous best of 13.07.10, set in 2007.
The old record stood at 13.03.93 which Carroll had set in Berlin back in 1998.
Cragg, 31, had clocked 13:45.33 in finishing 14th at the recent World Championships in Daegu.
Friday's race was won Imane Merga of Ethiopia in 12.58.32.
Diamond League 5,000 metres: 1 Imane Merga (Ethiopia) 12:58.32; 2 Thomas Longosiwa (Kenya) 12:58.70; 3 Vincent Kiprop Chepkok (Kenya) 12:59.50; 4 Tariku Bekele (Ethiopia) 13:01.85; 5 Alistair Cragg (Ireland) 13:03.53; 6 Albert Rop (Kenya) 13:03.70