Both the audience and English tennis pro Andy Murray showed their displeasure after the referee's mistake.
Francisco Cerundolo, ranked 27th, had just won a key point when he was chasing in the first set.
But at one point the ball had bounced twice on the ground before hitting it back.
When the replays were shown in the arena, the crowd started.
Then Cerundolo stepped forward until the referee awarded the point to Murray.
- Incredible scenes at an important stage of the match, says BBC Sport's Jonathan Jurejko.
- Cerundolo gets the thumbs up from Murray and warm applause from the audience, he continues.
See the event in the player above.