Australia's No.1 was given a code violation by umpire Ana Carvalho in the fourth set of what was turning into an uncomfortably difficult match against Belgian qualifier Kimmer Coppejans on Thursday, before he eventually prevailed 6-7 (5-7) 6-3 6-3 7-6 (7-2).
The normally placid de Minaur admitted he had been edgy during a match which had stretched over two days because of rain delays, and was also concerned after girlfriend Katie Boulter's match had been interrupted earlier on Wednesday on the same court 18 by a confetti-throwing protester.
De Minaur, who's based in Alicante and speaks the language fluently, knew that the Brazilian umpire could also speak it too after they'd had an earlier conversation, the Australian accepting that he'd merited the warning when he got frustrated and shouted out an expletive in Spanish.
"To be honest, I deserved that," he admitted. "I was a bit on edge and I just didn't think.
"I'm not surprised actually, because the chair umpire talked to me in Spanish before the match, so I knew as soon as I said it that I was going to get done. It wasn't very smart."
His frustration had begun on Wednesday when he and Coppejans, a former French Open boys' champion who had battled through three rounds of qualifying, were called on to court late to start their first-round match after two days of downpours.
"I was probably a little bit on edge. It's never easy walking out on court at 6.45pm, 7pm, knowing that there is a good chance you might not finish the match," said de Minaur.
"The court is quite dewy, quite slippery. It's completely different to playing during the day. If you don't finish, you know you've got to come back the following day."
The Just Stop Oil protests were still in the back of his mind.
"It was pretty, pretty crazy," he said.
"We've had not the best weather the first couple days and then out of all the courts they could have protested on, it was on my court!"
Asked if he felt a third protest might take place in his match too, he said: "You would never say never. But I was sure hoping it was not going to happen."
De Minaur resumed on Thursday two sets to one up but should have been taken to a fifth set when 29-year-old Coppejans, who played a terrific match for someone ranked 181 in the world, nervily struck an easy forehand put-away long.
De Minaur went on to prevail in three hours 24 minutes to set up a second-round meeting with 2021 finalist Matteo Berrettini, who defeated fellow Italian Lorenzo Sonego despite having been struggling with an abdominal issue.
"He's obviously a very dangerous player who has played some great tennis here," said de Minaur.
"He's got a massive serve, massive forehand, a great slice. So very tricky, tricky opponent. He is one of those unseeded guys that you probably didn't want in your section.
"But hey, I knew this coming in. I knew I had a tough section. So I'm looking forward to the battle. Should be fun."
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