Novak Djokovic had the sympathy of conqueror Denis Istomin after the Uzbek's sensational victory over the defending champion, with the unheralded wildcard thanking his mum for her role in his exploits at the Australian Open.

Djokovic's hopes of winning the first grand slam of the year for a record seventh time were ended when Istomin pulled off a huge upset by winning 7-6 (10-8) 5-7 2-6 7-6 (7-5) 6-4 in the second round on Thursday.

The World number 117 has never been beyond the fourth round in a major and was not expected to trouble Djokovic at Melbourne Park, but the outsider took his game to another level.

And the 30-year-old, who is coached by his mum Klaudiya Istomin, said he surprised himself after sending the 12-time grand slam champion packing.

"I feel sorry for Novak. I was playing so good," he said in his on-court interview.

"I surprised myself as well. I want to thank my team, mum, you do a good job."

He added: "So much emotion in my mind I cannot hold it. I want to say thank you very much for coming and supporting me.

"It was tough. Since the third set I get cramp in my leg so I don't know how I held it. 

"It is the biggest win for me. It means so much so now I can feel I can play with these guys and be with them on the same level."

Next up for Istomin is a meeting with Pablo Carreno Busta.