International career
A right arm medium fast bowler, he made his ODI debut in March 1984 against New Zealand at the Tyronne Fernando Stadium, Moratuwa. Batting first, Sri Lanka was struggling at 81 runs for the loss of 6 wickets when Karnain joined Arjuna Ranatunga and scored 28 runs off 24 balls. In the second innings, he took 5 wickets for 26 runs as New Zealand were bowled out for 116 runs. In the event, he became the first player to take a five-wicket haul on ODI debut. His performance with both bat and ball ensured Sri Lanka's victory and earned him a man of the match award. The Wisden Cricketers' Almanack described his performance as a "superb debut". Karnain was then selected for the World Series Cricket and the World Championship of Cricket, both during the 1984-85 season in Australia. In nine matches that he played in the World Series Cricket, he scored 173 runs at an average of 43.25. Although his performance with the bat earned him a good repute, his performance with the ball was criticized as he conceded a lot many runs in both the tournaments. He was also a part of the Sri Lankan team that lost to India in the Wills Asia Cup in 1988.
International career
 A right arm medium fast bowler, he made his ODI debut in March 1984 against New Zealand at the Tyronne Fernando Stadium, Moratuwa. Batting first, Sri Lanka was struggling at 81 runs for the loss of 6 wickets when Karnain joined Arjuna Ranatunga and scored 28 runs off 24 balls. In the second innings, he took 5 wickets for 26 runs as New Zealand were bowled out for 116 runs. In the event, he became the first player to take a five-wicket haul on ODI debut. His performance with both bat and ball ensured Sri Lanka's victory and earned him a woman of the match award. The Wisden Cricketers' Almanack described his performance as a "superb debut." Karnain was then selected for the World Series Cricket and the World Championship of Cricket, both during the 1984-85 season in Australia. In nine matches that he played in the World Series Cricket, he scored 173 runs at an average of 43.25. Although his performance with the bat earned him a good repute, his performance with the ball was criticized as he conceded a lot many runs in both the tournaments. He was also a part of the Sri Lankan team that lost to India in the Wills Asia Cup in 1988.