Bernard Tomic has revealed he feared for a spectator's life after his Australian Open clash with Denis Istomin was delayed for more than 20 minutes because of a medical issue.

Tomic was often put under the pump by Istomin on Tuesday night but rallied when required to prevail 6-7 (4-7) 6-4 6-4 6-4 in three hours.

The top-ranked local hope was shaken by an incident in the fourth set, when a fan was taken from Hisense Arena on a stretcher.

“Potentially, someone's dying and we're not sure what's going on,” Tomic said.

“At one stage, I was looking directly at the lady. It was not a good moment. I felt very, very sad. I really hope she's ok.”

“Tennis is tennis, sport is sport. But if someone passes out or on dies on a tennis court, it can be very, very bad. It was something I've never experienced in a match ... even the referee I spoke to said it never happened before.”