Andy Murray suggested opponent Fernando Verdasco was lying after a row over illicit coaching erupted following their second-round clash at the US Open.
The high temperatures and humidity in New York this week led tournament organisers to introduce a new rule permitting a 10-minute break between the third and fourth sets during men's matches.
Players are not allowed to talk to their coaches, which is exactly what Murray said he saw Verdasco doing after finishing a cold shower after he was beaten 7-5 2-6 6-4 6-4.
As Murray was bowing out No.1 seed and defending champion Rafael Nadal has powered into the third round with a straight-sets win over Vasek Pospisil.
Nadal hit a barrage of winners and mixed in lobs and drop shots to confound the unseeded 28-year-old Pospisil, ranked 88th.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
The Spaniard got an early break in the third set and raced ahead to a 6-3 6-4 6-2 victory.
He'll face 27th-seed Karen Khachanov, 22, of Russia in the third round.
Murray was furious that it was he who alerted officials to the incident, telling umpire Nico Helwerth when he returned to the court: "I had to tell them because no-one knows the f***ing rules.
"I went and told the supervisor. I said, 'what are you guys doing? I mean, there's clear rules here and you're allowing this to take place. I don't get it.'
"Then he ran through, 'oh, you're not allowed to speak.' They obviously weren't in there for long, but you've got to do better than that. This is one of the biggest events in the world."
Verdasco flatly denied any such rule breach had taken place, claiming that while his coach was in the locker room, he spoke only to another player, Marcos Baghdatis, and the Cypriot's coach.
He said: "Obviously if Andy says that, I don't want to say that he lies, but I didn't talk one word with my coach or any one member of my team. I know exactly the rule and I don't want to be the one breaking it."
With tournament organisers apparently unable to shed any light on what happened, it was a case of one man's word against the other - and Murray was determined to make sure it was he who had the last one.
In a post on Instagram, Murray wrote: "I'm off to get a health check as apparently I've started imagining things," followed by the hashtag #liarliarpantsonfire.
Nick Kyrgios, who has history with Verdasco, also weighed in on the debate, saying of the coaching accusations on Twitter: "Let's be real, very believable because it is Verdasco lol."
Stan Wawrinka fought off French qualifier Ugo Humbert to earn a 7-6 (7-5) 4-6 6-3 7-5 victory and a place in the third round.
The 33-year-old now faces 25th seed Milos Raonic after the big-hitting Canadian blasted past Frenchman Gilles Simon 6-3 6-4 6-4.
Russia's unseeded Daniil Medvedev upset 15th seed Stefanos Tsitsipas 6-4 6-3 4-6 6-3.
Fifth-seed Kevin Anderson advanced with a 6-2 6-4 6-4 victory over France's Jeremy Chardy.
John Isner reached the third round for the seventh consecutive year, beating 42nd-ranked Nicolas Jarry of Chile 6-7 (7-9) 6-4 3-6 7-6 (7-2) 6-4.
