Daniil Medvedev was issued with a code violation in the first set against Carlos Alcaraz after appearing to say something in frustration at the chair umpire.
The first set between Medvedev and Alcaraz was proving to be an entertaining affair with both players breaking the other's serve.
Medvedev was on top though as he kept the unforced errors to a minimum and put himself 5-2 up.
Alcaraz forced his opponent to try and serve out for the match at 5-3 with the Spaniard stepping it up to bring the match back on serve.
Daniil Medvedev was given a code violation
BBC
The defending champion was given the break by virtue of the chair umpire stepping in to rule that the ball had bounced again before Medvedev got his return over the net.
The appeared to infuriate the No 5 seed, who lashed out at the chair umpire before taking his seat.
The chair umpire was then seen calling both the referee and supervisor onto court to seemingly seek advice on what Medvedev had said to her.
It was then announced that Medvedev was given a code violation for unsportsmanlike conduct.
The incident caused some confusion as Tim Henman suggested Medvedev was lucky to stay on the court.
"If you use a swear word you get a code violation and a fine," he said.
"But, if you verbally abuse the umpire that's where there is a question mark.
"Maybe a default, but with the supervisor on court and the umpire down that doesn't happen if something has not gone on.
Daniil Medvedev said something to the umpire
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"That was an interesting moment," Henman said.
Medvedev will now be docked a point if he receives a second code violation in the match.
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Daniil Medvedev ended up taking the first set
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There was nothing to separate the two in the end of the first set, which went to a tiebreak.
But Alcaraz found himself on the backfoot early on after losing his first two serves with Medvedev opening up a 5-0 lead.
The Russian star then took full advantage of his healthy lead to take the first set tiebreak.