Collins, who had only been knocked down twice previously in his professional career, found himself on the canvas after just 12 seconds as the Cummings launched a furious early attack which caught the Irishman cold as he emerged for what he believed would be a routine defence.
Collins recovered to put the American down with a thunderous right hand before the first three minutes were out and, despite another brief shaky spell in round two, the champion eventually made his punches tell a round later to keep on track for a much-touted unification bout.
Until that point, Cummings, a 29-year-old fireman from Kansas who was taking a considerable step up in class, had given as good as he got and had briefly even threatened to extinguish Collins's flame.
Collins admitted as much afterwards. "I learned the hard way that you cannot underestimate anyone in this game," said the champion. "They told me he was a big puncher and they were right. He hit me hard, as hard as anyone, and I have been in with some big hitters like Nigel Benn and Chris Eubank."
Collins looked strangely vulnerable at times, was ragged in his work and seemed agitated when some his better hooks and crosses did not affect the challenger.
The Kelvin Hall crowd gave the Dubliner a wonderful reception which will make future defences in the city inevitable. But they were stunned into silence when Collins, who looked a little off-balance, was knocked off his feet by a quick combination. Cummings had certainly come to fight. Collins, though, leapt to his feet and before the first bell he had wrested back the initiative.
In round two Cummings still came forward but it became apparent that the fight would not last much longer and when Collins floored Cummings in round three then backed him into the ropes, the referee, George Francis called a timely halt.