Again, the humor here is edited out. The word translated as "came/went" is a special word for people approaching someone in a superior position, which is how Jesus always uses it except in this story. The idea is that the sons, even the second son, saw themselves as better than their father.
In the Greek, the son does not say "I go" or "I will." He simply says "I" in the form of a subject, followed by the word for "master" or "lord." When a Greek subject appears without a verb, the verb "to be" is assumed, so the sense of what he said is "I am, master," which certainly gives the sense of agreement. Why does he speak this way? Because he is not lying as he would be if he said "I go" or "I will." This allows Jesus's opponents to see his answer as the best. He did not lie and he did not deny his father's will.
NOTE: Found a number of different sources for this and the previous verse that did not agree.
Christ's Words in Matthew as a Guide to 40 Days of Prayer.