Bencic is hitting her low, flat groundstrokes confidently and the strength of her backhand - both crosscourt and down the line - particularly caused problems for Gauff.

Bencic's improved fitness also showed in the decider. She fought back from 40-0 down to break Gauff for a 5-4 lead in the decider, serving out victory after two hours and 20 minutes.

"Obviously it's not easy after maternity leave to do all the work again," said Bencic, who faded in a three-set defeat by Gauff at the Australian Open in January.

"You feel like physically you're doing stuff from zero and it's just your body changing so much in a short period of time.

"It was really difficult, but I definitely feel like physically, I am there like before [maternity leave]."

Bencic is only the sixth wildcard to reach the women's last eight at Indian Wells since the tournament began in 1989.

Next she will face Australian Open champion Madison Keys in the last eight, who beat Wimbledon semi-finalist Donna Vekic 4-6 7-6 (9-7) 6-3 for her 15th consecutive win.