Weeraratne, 24, created the record on Tuesday playing for Ragama cricket club against Kurunegala in Sri Lanka's premier limited-overs tournament.
The effort surpassed England all-rounder Adam Hollioake's half-century off 15 balls for Surrey against Yorkshire at Scarborough in 1994. Weeraratne ended on an unbeaten 66 off 18 balls, an innings studded with eight sixes and two boundaries.
ONE-DAY CRICKET'S FASTEST HALF-CENTURIES (BALLS FACED):
12 - K. Weeraratne, Ragama v Kurunegala, Colombo, 2005
15 - A. Hollioake, Surrey v Yorkshire, Scarborough, 1994
16 - G. Rose, Somerset v Glamorgan, Neath, 1990
16 - M. Fleming, Kent v Gloucestershire, Canterbury, 1996
16 - M. Fleming, Kent v Scotland, Glasgow, 1991
17 - S. Jayasuriya, Sri Lanka v Pakistan, Singapore, 1996.