Mikhail Kukushkin and Aleksandr Nedovyesov gave Kazakhstan a commanding 2-0 lead over hosts Australia after the opening singles of their Davis Cup World Group quarter-final in Darwin on Friday.
Kukushkin gave the Kazakhs the early momentum with a straight sets 6-4, 6-3, 6-3 win over teenager Thanasi Kokkinakis in just over two hours.
World No. 115 Nedovyesov then stunned the 41-ranked Nick Kyrgios 7-6 (7/5), 6-7 (2/7), 7-6 (7/5), 6-4 to put Kazakhstan on the brink of reaching the Davis Cup semi-finals for the first time.
It was Kyrgios`s first loss in three matches on grass in the competition.
Australia must win Saturday`s doubles encounter to keep the tie alive in Sunday`s reverse singles.
Kyrgios, who was heavily criticised by the Australian media amid claims of "tanking" during his fourth-round loss to Frenchman Richard Gasquet at Wimbledon, and also for arguing with umpires and sarcasm during his press conferences, admitted the loss had left him drained.
"Physically, I felt OK. I felt like my body was good. But mentally, I almost felt a bit drained out there," Kyrgios said.
"It was hard to focus. It was hard to dig deep. It was hard to push myself because a lot has gone on."
The disappointing outcome capped a forgettable day for Australian tennis after Bernard Tomic was arrested in the United States overnight.
Tomic was taken into custody after failing to follow police orders to leave his hotel penthouse in Miami following a night of loud partying.
Tomic should have been with the Davis Cup team in Darwin. But he was dumped from the squad following his outburst against Tennis Australia`s hierarchy and former Davis Cup captain Pat Rafter at this month`s Wimbledon.
With Tomic unavailable, Kokkinakis, who was preferred to big-serving Sam Groth, was handed responsibility for opening the tie against Kazakhstan`s top-ranked player.
"I wasn`t able to find my game. And when I found it in the second set, I got broken straight back, which killed me," Kokkinakis said. "I didn`t find my rhythm today."
"I`m taking it pretty hard at the moment. I`m pretty disappointed."