All-rounder Jan Frylinck smashed 44 runs and took two wickets as Namibia hammered Asia Cup champions Sri Lanka by 55 runs to cause a major upset in the T20 World Cup opener in Geelong.

The left-handed Frylinck and JJ Smit, who made an unbeaten 31, lifted Namibia to 163-7 with their 69-run seventh-wicket stand, after being invited to bat first in Geelong.

Sri Lanka were then bowled out for 108 in 19 overs with David Wiese, Frylinck, Bernard Scholtz and Ben Shikongo taking two wickets each in the team's first of three opening-round matches.

The African minnows are on course for a second straight Super 12 place after achieving the feat on their T20 World Cup debut last year in the United Arab Emirates.

Namibia lost their openers inside three overs with returning fast bowler Dushmantha Chameera getting a wicket third ball when Michael van Lingen was caught at deep third-man.

Jan Nicol Loftie-Eaton fell to a brilliant diving catch by wicketkeeper Kusal Mendis after a 12-ball 20.

Stephan Baard and skipper Gerhard Erasmus attempted to rebuild with a stand of 41 but Sri Lanka's bowlers kept chipping away with wickets.

Namibia slipped to 93-6 when spinner Maheesh Theekshana got big-hitter David Wiese caught behind for nought but Frylinck, who hit four fours in his 28-ball innings, and Smit had other ideas.

The pair took the attack to the opposition with five fours and two sixes in the final five overs.

Sri Lanka, who won the Asia Cup last month, lost Kusal Mendis for six when his top-edge off Wiese ballooned up to land in the gloves of Zane Green.

Ben Shikongo silenced the Sri Lankan fans when he sent back Pathum Nissanka for nine and Danushka Gunathilaka for nought on consecutive balls.

Bhanuka Rajapaksa played out the hat-trick ball, surviving a big lbw shout.

Frylinck, a left-arm seamer, then got Dhananjaya de Silva as Sri Lanka slipped to 40-4.

The left-handed Rajapaksa and skipper Dasun Shanaka, who made 29, attempted to put the chase back on track with a partnership of 34 but Bernard Scholtz broke the stand with his left-arm spin.

Scholtz got Rajapaksa out for 20 when he skied a shot and soon sent back Wanindu Hasaranga.

Frylinck ended captain Shanka's resistance and the lower order soon followed to spark joyous celebrations when Wiese claimed the final wicket.