McEnroe did not disappoint in keeping things lively. (Getty Images)

When John McEnroe and Andy Cohen collide on Watch What Happens Live, Cohen's unabashedly trashy late-night talk show, it's a given that the conversation will head into unexpected terrain. Add fellow guest Amy Sedaris, and audiences know this is an episode that should not be missed.

The largely-reformed hothead known as Johnny Mac did not disappoint in keeping things lively, when prompted and of his own volition. In the live after-show, not aired on Bravo TV proper but appearing online, he was asked by the evening's final caller what he made of Serena Williams' showdown at the 2018 US Open with chair umpire Carlos Ramos.

"I thought he went overboard," McEnroe, who was not calling the match live for a TV broadcast at the time, said of Ramos. "I didn't like what he did to her, even though it was a lose-lose [situation]. Because she f—ed up and he f—ed up."

In the true episode that did run on Bravo, McEnroe was put to the test of Cohen's patented "Plead the Fifth" game, in which participants must answer a series of fairly probing questions, electing not to answer just one of the three posed. He took the bait when asked if he would beat Serena in a match these days, saying that though his daughters disagree with him, "I've got to be honest, I still think I have a chance to win."

The 60-year-old tennis legend offered rather readily that his most well-endowed foe over the years was one Ivan Lendl, though it "pained" him to say so. McEnroe chose to play his "stay mum" card when interrogated as to what famous older woman he had an affair with, as described in his book You Cannot Be Serious.

It was almost an episode of WWHL devoid of Real Housewives blather. No so fast, though, as McEnroe confessed at one juncture that, in another life for each of them, he had once dated Sonja Morgan of Real Housewives of New York infamy.

McEnroe was on Cohen's show to promote the New York–based "You Cannot Be Serious!" comedy event benefiting his Johnny Mac Tennis Project, a nonprofit organization supporting youth in sports. Cohen and Broadway-minded comedian Mike Birbiglia are co-hosting the event alongside McEnroe, with additional comedians being announced up to the April 10 event date. McEnroe's goal is to make tennis more accessible and perhaps even groom a future major champion. 

Follow Jon on Twitter: @jonscott9