Coco Gauff lost her cool in a HUGE way Tuesday, smashing the hell out of her racquet after she got her butt kicked in straight sets at the Australian Open.

The American tennis phenom was beaten handily by Ukraine's Elina Svitolina 6-1, 6-2 in the quarterfinals of the grand slam tournament in Melbourne.

After Coco stomped off the court, she went to town on her tennis racquet out of sight of the crowd at the Rod Laver Arena ... but a photog managed to catch her temper tantrum.

Check out video of the stunning moment ... Coco just goes nuts, smashing the racquet to smithereens on a concrete ramp.

Definitely not Coco's best moment ... but she'll bounce back for sure ... Remember, she's ranked No. 3 in the world in women's tennis, and she's won two Grand Slams in the singles division -- the 2023 US Open and the 2025 French Open.

As for Svitolina, she's squaring off against Aryna Sabalenka -- who's ranked No. 1 -- in the semifinals of the Australian Open. Svitolina clocks in at No. 12 on the ranking list, so it should be one helluva match!