All three were interested in readymades, to varying degrees. All three were also dealing with very personal responses to Pollock. Like Steve Lacy, they (and many of their contemporaries) saw Pollock as "a way to the other side."
It's interesting to take someone like Kenneth Noland, whom Greenberg championed, and place him side-by-side with Johns' targets and Stella's stripe paintings and shaped canvases. The tension between recognizable imagery and color-defining-form is pretty fascinating.
And Stella, fwiw, was first influenced by his house-painting jobs in New England, dealing with the patterns of wooden siding in barns and houses. You can see the evolution from his 1958 work up through the Benjamin Moore series, though the copper and aluminum works veered somewhat by being shaped.