Mirra Andreeva admitted she was "not really proud" of how she handled her defeat to Katerina Siniakova in the round of 32 at the Indian Wells Open.

Siniakova defeated the reigning champion 4-6 7-6 (7-5) 6-3 in a near three-hour thriller, leaving Andreeva frustrated with herself both during and after the loss.

Andreeva recovered from a slow start in the first set, where she was 3-0 down, to take the lead after converting three break points.

The pair then exchanged consecutive breaks on three occasions in the second, though Siniakova got the better of Andreeva in the tiebreak, which was finely poised at 5-5.

That led to Andreeva first throwing her racket at her chair before smashing it completely on the ground, and her anger brewed throughout the third as Siniakova pulled off the comeback victory.

Andreeva was seen shouting expletives towards the stands as she left the court, but she insisted that it was not at anyone in particular.

"It was to myself, to everyone, basically. I mean, after the loss, I just get very angry, so I say those things sometimes to myself," said the 18-year-old.

"I mean, first to myself, of course, but then, yeah, it was just anger coming out, just a lot of emotions. Not really towards anyone.

"I can say that there were a lot of emotions that I was going through after the loss.

"But of course I'm not really proud of how I managed it. I'm not really proud of how I handled it in the end.

"Those are the things that really need to work on soon. I don't know. Not in the future but whenever I get the chance. I hope that I can work on it and I get better in that, as well."

Since the Tier format's introduction in 1990, Siniakova is the first player to defeat multiple reigning Tier I/WTA-1000 champions while ranked outside the WTA top 40 – also doing so in Wuhan in 2018.

And there was another upset in California, with Great Britain's Sonay Kartal coming from a set down to beat Madison Keys.

Kartal won 2-6 6-2 6-3 against Keys, who was playing in her first match since her last 16 defeat at the Australian Open in January.