Sri Lanka were crowned Asia Cup champions last month, but they were brought back down to earth in the Group A opener at Kardinia Park on Sunday (October 16).
Frylinck top scored with 44 off 28 balls as Namibia recovered from 35-3 to post 163-7 in Geelong, JJ Smit also making a quickfire unbeaten 31 down the order.
Sri Lanka were all out for only 108 in reply after they were reduced to 21-3 inside four overs, captain Dasun Shanaka (29) one of only four players to make double figures.
All-rounder Frylinck claimed 2-26, with David Wiese, Bernard Scholtz and Ben Shikongo also took two wickets apiece in an excellent display in the field from Namibia in their quest to reach the Super 12 stage for the second successive World Cup.
Sri Lanka had been forced to make a last-minute change to their squad, replacing the injured Dilshan Madushanka (quad) with fellow paceman Binura Fernando.