The 2014 winners had to play the qualifying round but Dasun Shanaka's team proved they were still too good for their opponents as they registered their second successive win to make the main draw.
Put into bat, Sri Lanka recovered from a precarious 8-3 and went on to post a commanding 171-7 with all-rounder Wanindu Hasaranga (71) and opener Pathum Nissanka (61) engineering their turnaround.
Ireland had promised a strong fight when they removed three Sri Lankan batsmen in the first 10 deliveries.
Paul Stirling dismissed Kusal Perera with his second ball and, in the next over, Josh Little dismissed Dinesh Chandimal and Avishka Fernando off successive deliveries.
Hasaranga not only denied Little a hat-trick but also led a counter-attack with his 47-ball blitz, which included one six and 10 boundaries, including four in a row against Simi Singh.
"Of course it was a concern at eight for three, but they (Hasaranga/Nissanka) put on an awesome partnership," Shanaka said.
"Hasaranga at five is a plan coming in at the World Cup and it worked well for us," he said of the all-rounder, who was named player-of-the-match.
Sri Lanka were more convincing with the ball and shot out Ireland for 101 in 18.3 overs with off-spinner Maheesh Theekshana (3-17) leading the rout.
Ireland struggled to get going in their reply and were 32-3 in the fourth over.
Andy Balbirnie waged a lone battle with a gritty 41 and the match was effectively over for Ireland when their captain sliced a Lahiru Kumara delivery to Fernando at backward point.
Earlier, in another Group A match, Namibia beat Netherlands by six wickets to register their maiden victory in the tournament.
David Wiese produced an unbeaten match-winning knock of 66 as Namibia, having restricted their opponents to 164-4, chased down the target with six balls to spare.
Netherlands are now out of the race and the winner of Friday's match between Namibia and Ireland will progress to the next stage.