Tennis Star Aryna Sabalenka Smashes Racket After Losing Australian Open, on Video

Aryna Sabalenka won't win her third Australian Open in a row ... and, while she usually wins the break point, she reached her breaking point after the heartbreaking L -- taking it out on her trusty racket.

The Belarusian tennis standout was playing American Madison Keys in the final ... and, ended up losing the third set 7-5, dropping two out of three after battling back down 1-0 to force a tiebreaker.

After a hard-fought final point, Keys emerged victorious ... walking up to Sabalenka to hug -- which the superstar did politely, if a bit stony-faced.

While Keys celebrated her victory by waving to the crowd, the real fireworks began near Sabalenka's bench ... where she repeatedly beat her racquet into the ground before spiking it away.

Watch the clip for yourself ... even the commentators sound a bit taken aback.

Sabalenka talked to the press about the blow-up after ... admitting it was caused by a bit of frustration -- stemming from how close she got to the three-peat.

This is Keys' first Grand Slam victory ... she fell just short of winning the 2017 US Open -- losing in the final to Sloane Stephens. Sabalenka -- as we mentioned -- has won two Australian Opens, and she won the US Open last year as well.