Prime Minister Hun Sen has ripped into the judges of Sunday's “fight of the century” between Filipino Manny Pacquiao and American Floyd Mayweather, slamming the result as “unbelievable”.

At the opening of a road in Pursat on Monday, the premier labelled the result “too bad” and expressed his dismay that the victory awarded to Mayweather.

“It was brilliant, my best friend,” he said sarcastically, referring to the United States.

“The whole world reacted; and it was not a small reaction, it was so big because Floyd [Mayweather] was always running and protecting but Pacquiao always beat him into the corner of the ring – I did not believe America was like that.”

All three judges unanimously awarded the 12-round bout to Mayweather with two scoring the fight at 116-112 in the American's favour and another 118-110.

Mayweather fought defensively, constantly evading the notoriously fast and aggressive Pacquiao but nevertheless, according to The Guardian, landed 67 more punches.

US embassy spokesman Jay Raman declined to comment on the premier's remarks on Monday.

Hun Sen has been fond of remarking during his career that “international standards exist only in sports” when faced with criticisms on issues such as human rights or democratic governance.