While Tiafoe giggled to himself, Krueger went over to the chair umpire, grabbed a ball and smashed it out of the court to where the scene of passion was playing out.
The love-making continued for a couple of minutes, prompting Tiafoe to yell out: "It can't be that good."
Initially, commentator Mike Cation thought someone in the crowd forgot to turn the volume down when playing a video on their phone.
"Well, that is the most bizarre situation," Cation said on the Challenger Tour live stream. "I don't know how to put this, folks, but somebody's phone is going off in the stands ... and it was an adult video."
But as the moans continued, Cation realised the X-rated romp wasn't playing out on a screen at all. "No, that's not a phone, that's an apartment across the lake," he said. "Oh my God."
Tiafoe was able to put the disturbance behind him and carried on to win the match in straight sets 6-3 6-2.
Sport has a rich history of fans getting it on, providing just as much action off the field as on it. In 1995 an ESPN cameraman caught two guys and a girl getting handsy with each other at Boston's Fenway Park in an incident dubbed the "Fenway threesome".
There must be something about baseball that just gets people going, because in 1997 a couple was seen getting up close and personal at the Oakland Coliseum during a game between the Oakland Athletics and Los Angeles Angels.
