Daniil Medvedev flew into a rage after winning his match against Stefano Tsitsipas at the Miami Open on Thursday.
Medvedev came from a set down to beat Greek opponent Tsitsipas 2-6 6-4 6-2, but the Russian took exception to something his opponent said to him after the post-match handshakes.
Medvedev could be heard saying: "Hey Stefano, do you want to look at me and talk? You don't look at me?
"You go in emergency toilet for five minutes, you hit a let and don't say sorry, you think you are a good kid? 'Look at me, look at me huh! You don't look at me?
"I answer him because he doesn't know how to fight, he's a small kid who doesn't know how to fight. If he says something to me and he wants to fight, he needs to do it. If he wants to fight I'm okay about it. I don't want to fight."
Medvedev, who pelted the umpire's chair with coins at Wimbledon last year, added: "I can be a very bad guy sometimes, but here, what did I do?"
In the day's other matches, Canadian teenager Denis Shapovalov managed to grind his way to a three-set first-round win over Viktor Troicki.
Shapovalov came through 6-3 6-7 (4-7) 7-6 (8-6) after wasting five match points against Troicki in a topsy-turvy clash.
The 18-year-old was handed victory when Troicki double-faulted to win a dramatic third-set tie-break.
There were also wins for Leonardo Mayer, Evgeny Donskoy, Guillermo Garcia-Lopez, Dusan Lajovic, and Steve Johnson.
In the women's draw, world No 1 Simona Halep survived a scare from France's Oceane Dodin, beating the lucky loser 3-6 6-3 7-5 to reach the third round.
Angelique Kerber, the 10th seed, cruised to a 6-2 6-2 win over Swede Johanna Larsson, setting up a third-round showdown with Russian 23rd seed Anastasia Pavlyuchenkova.
Fifth-seeded Czech Karolina Pliskova dispatched Russian Ekaterina Makarova 7-5 7-5 and unseeded German Carina Witthoft upset her 12th-seeded countrywoman Julia Goerges 7-6 (7-2) 4-6 6-4.
You can watch more ATP Masters 1000 action from the Miami Open when we continue our coverage on Sky Sports Arena on Friday at 3pm.
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