Australia shrugged off the last-minute pullout of captain Mitchell Marsh to post 182-6 in 20 overs, after stand-in skipper Travis Head won the toss and elected to bat first on a slow and spin-friendly wicket at the R Premadasa Stadium.
Ireland's chase got off to the worst possible start when captain Paul Stirling pulled up injured after darting for a run off the first ball, his premature retirement leaving them a man down in Colombo.
Harry Tector perished for a duck in the second over, bowled by Matthew Kuhnemann, before Ross Adair failed to make the most of his reprieve following a drop by Matt Renshaw and was bowled out by Ellis for 12 to leave Ireland in deeper trouble.
The writing looked to be on the wall when Ellis had Curtis Campher caught at mid-wicket for four, before he had Ben Calitz bowled for his third wicket inside the powerplay to leave Ireland reeling at 27-4.
Zampa (4-23) then made his mark as he picked up the next four wickets, including middle-order batter George Dockrell, who gave Ireland hope with a quick-fire 41 off 29 before he was stumped off a wide delivery when he gave the spinner the charge.
Barry McCarthy was caught at deep mid-wicket to give Ellis (4-12) his fourth wicket and with Stirling unable to bat again, Ireland were all out for 115.
61-run stand
Earlier, Josh Inglis went all guns blazing during his 17-ball 37 as Australia accumulated 64 runs in their six powerplay overs for the loss of Head and Cameron Green (21), but Ireland's bowlers were in no mood to let the match slip away.
Some tight spells of bowling turned the screws on Australia, but a workmanlike 61-run stand between Renshaw (37) and Marcus Stoinis (45) for the fifth wicket laid a solid platform for the 2021 champions to build on.
Australia were rocked again when Renshaw was bowled by a quicker one from Matthew Humphreys, while Stoinis survived being dropped at cover before perishing in the 18th over, bowled by Mark Adair (2-44).
Lower-order batsmen Cooper Connolly and Xavier Bartlett (both 11 not out) then took Australia past the 180-run mark, a score that proved decisive in the end and ensured Australia sealed a comfortable victory to top Group B.