"On his first serves, to try to anticipate and read his serve, where he's going to go 140 miles per hour down the T and also pretty good angle wide, it's hard to position yourself well... it is a gamble," the 12-time grand slam winner told the ATP World Tour website.

"His second serve, if you think you're going to have a look at it, you don't, because he goes for it as well. He didn't make too many double faults."

Kyrgios' win ends Djokovic's impressive 19-match winning streak at Indian Wells, where he won three years in a row from 2014.

Despite Wednesday's disappointing loss, Djokovic was proud of his amazing run in California.

"The run was amazing... I am very proud of it, obviously," he added.

"It had to end at some stage. Unfortunately, it was today. Nick, again, as he did in Acapulco earlier, a few weeks ago, he served so well.

"Just wasn't managing to get a lot of balls back on his serve, first and second, as well. That's what made a difference. He obviously comes out playing his style, very aggressive, and just going for every serve, whether it's first or second. It's obviously very hard to play like that."

Kyrgios faces Australian Open champion Roger Federer in the quarter-finals on Friday.