Daniel Wiffen (23) became the first Irishman to win an Olympic swimming gold when he powered home first in the men's 800m freestyle in Paris on Tuesday.
Wiffen hit the wall in 7min 38.19sec, the fifth-fastest time ever, ahead of American defending champion Bobby Finke (7:38.75) and Tokyo silver medallist Gregorio Paltrinieri (7:39.38) of Italy.
World champion Wiffen took control at 400m after Australia's Elijah Winnington went out hard but tired as the Irishman reeled him in.
Paltrinieri made at a move at 600m and led to the final turn before Wiffen came roaring back to make history for his nation.
The only other gold won by Ireland in an Olympic pool came at Atlanta in 1996 when Michelle Smith collected three.
Wiffen will also contest the 1,500m freestyle and the 10km open water swim.