Brisbane QLD, Australia, 5 January 2018 | Laine Clark

Australian No.1 Nick Kyrgios has dug deep to move through to the Brisbane International semi-finals after a come from behind 1-6 6-3 6-4 victory over Ukraine’s Alexandr Dolgopolov.

World No.21 Kyrgios – ranked 17 spots higher than his opponent – looked lethargic early with his troublesome left knee strapped as former Brisbane finalist Dolgopolov broke twice to clinch the first set in 22 minutes.

But the dual grand slam quarterfinalist held his nerve to book a semi-final showdown with the winner of Friday night’s clash between top seed Grigor Dimitrov of Bulgaria and Briton Kyle Edmund.

Third seed Kyrgios, 22, did not look comfortable from the outset with his left knee strapped after tweaking it in his second-round win over fellow Australian Matthew Ebden.

Dolgopolov took full advantage to cruise through the first set before Kyrgios appeared to flick a switch in the second.

He broke the Ukrainian in the second game and claimed the second set in just 29 minutes.

Kyrgios then secured a vital break in the seventh game of the third set before clinching the come from behind victory in 90 minutes at Pat Rafter Arena.