Mirra Andreeva’s Indian Wells title defense met a bad-tempered end on Monday as Katerina Siniakova stunned the Russian teenager 4-6, 7-6, 6-3.

The 18-year-old opened her bid to retain her crown with a dominant 6-0, 6-0 demolition of Solana Sierra. But she was in trouble early and often against Siniakova, the world No 44, in a rollercoaster contest that ended with a shot from the Czech that hit the net cord and dribbled over in one last frustrating moment.

Andreeva threw her racket as she approached the net before gesturing and appearing to swear at the crowd several times as she left the court.

“I’m not really proud of how I managed it,” said Andreeva, but added the profanities picked up by courtside microphones weren’t directed at the fans.

“It was to myself, to everyone, basically,” said Andreeva. “I mean, after the loss, I just get very angry, so I say those things sometimes to myself. 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.”

Andreeva has admitted she has struggled to contain her emotions throughout her young career, and after Monday’s loss she said it was an area she needs to address.

“Those are the things that [I] really need to work on soon,” she said. “I don’t know. Not in the future but whenever I get the chance. Yeah, I hope that I can work on it and I get better in that, as well.”

Siniakova, a former doubles number one, admitted the net cord shot was an awkward way to seal the win in a match that featured seven service breaks for each player and 43 break chances between them.

“Of course I’m happy [the ball] went on the other side,” she said. “I was, like, should I cheer? It’s a really tricky finish. But definitely I will not say I’m not happy.”

Andreeva’s gestures after the match were not her first outburst of the day. She threw her racket after losing the second set tiebreaker before smashing it, resulting in a code violation. She regrouped to break Siniakova for a 3-2 lead in the third, but Siniakova won the next four games, saving two break points in the final game before gaining the win on her first match point.

Siniakova will face Elina Svitolina for a place in the quarter-finals after the ninth-seeded Ukrainian beat American Ashlyn Krueger 6-4, 6-2.