According to the newspaper report, Marian suggests that her ex-husband (Greer) was resentful of her remarriage and had killed her present husband. This, together with Greer's obsession with his former wife (keeping her clothes and photos) would surely indicate that he was aware of the new husband. Therefore he would know his name.
Tommy called Stanton's number and spoke to the maid who told him that Stanton would be home the next evening to watch the fights. Before hanging up and ending the call, Tommy repeated "Tomorrow". The next scene was him being greeted by Stanton as he let him in his house, with Stanton saying, "You're the young man who called this afternoon" when he should've said, "You're the young man who called yesterday" since Tommy wasn't supposed to be there until the day after he called.