Forever emboldened by his ratings superiority, O'Reilly's shots were mostly directed at the size of MSNBC's audience.
"With all due respect to Ms. Stefano, she isn't going to win by going on that channel," O'Reilly said. "Virtually no one watches it and they're not going to support their position, the few who do."
O'Reilly and his guest, Juan Williams, both agreed that Hayes brought Stefano on his show simply to embarrass her.
And true to form, O'Reilly never mentioned Hayes by name. Fox's culture warrior always avoided using Keith Olbermann's name during their bitter feud that dominated the aughts.
Ever since the two began sharing the 8:00 p.m. time slot last year, Hayes hasn't hesitated to go after O'Reilly.
After O'Reilly denounced the "race hustlers" who criticized Paul Ryan's comments on inner city poverty, Hayes promptly responded last week that O'Reilly is a "pretty accomplished race-baiter himself."
In February, Hayes questioned O'Reilly's claim to be a self-made man. O'Reilly swiftly responded — without mentioning Hayes' name, of course.
Hayes picked apart O'Reilly's argument in January that pot users largely avoid the threat of an arrest. And last summer, Hayes countered in painstaking detail what he described as O'Reilly's "super racist rant" on black culture.
The back-and-forth is vaguely reminiscent of the bitter Olbermann-O'Reilly rivalry that helped set MSNBC on its ideological course.
Olbermann's caustic attacks on O'Reilly brought prominence to MSNBC, which enjoyed a ripe period toward the end of George W. Bush's presidency stretching into the Obama year. Today, its ratings and revenue are both in decline.
Shortly before his show premiered in primetime last year, Hayes insisted that he didn't necessarily think he was in competition with O'Reilly.
"You know, obviously what O'Reilly does is remarkably successful from a ratings perspective, but I also think - I think there is a tremendous amount of inherited wisdom about what works in cable news, some of which is perceptive and wise and a lot of which is just not grounded in any real rigorous analysis or empirical analysis," Hayes told NPR.
"And so when people say, well, you're up against Bill O'Reilly, I just - it's really unclear to me - it's genuinely unclear to me whether that's true in any real sense, which is to say if we are competing for the same pool of viewers."
In the same interview, Hayes said he's not one to "hate-watch things" like some liberals who tune in to the "O'Reilly Factor."
He may have discovered that MSNBC's pool of viewers is filled with people who actually do like that sort of thing.
This post has been updated.