Hewitt grew up in Adelaide and has long used this tournament to get valuable match practice ahead of the year's first Grand Slam, but he played poorly against the world number 94 and Kunitsyn took the match 4-6, 7-6 (7/4), 6-4.

Hewitt joined defending Adelaide International champion Florent Serra on the sidelines after Serra was forced to retire during the third set of his match against fellow Frenchman Gilles Simon due to a heat-related illness.

Serra had just broken back to level the match at 5-7, 6-2, 1-1 in the third set when he withdrew.

Sweden's Joachim Johansson goes through to the quarterfinals as a result, having beaten Simon in their meeting Wednesday in the ATP's new round robin format.

The withdrawal highlighted the heatwave conditions endured by the players here this week, with temperatures reaching 37 degrees Celsius (almost 99 degrees Fahrenheit) in the city during the afternoon.

Unseeded Australian Chris Guccione used local conditions to his advantage when he beat Frenchman Arnaud Clement 7-6 (7/4), 7-6 (7/5) to reach his first ATP tour quarter-final.

Guccione said his win over Clement was one of his best.

"It's definitely up there. I've beaten Juan Carlos Ferrero a couple of times and a couple of guys in Davis Cup who are quite high, but other than that I've beaten three top 100 players in a row now, so I've never done that before," he said.

Vince Spadea of the US, who defeated Russia's Evgeny Korolev 6-1, 7-6 (8/6), also progressed Thursday to the quarterfinals,

So did Argentina's Juan Martin del Potro after he upset eighth seed Paul-Henri Mathieu 7-6 (7/3), 0-6, 6-3.

French second seed Richard Gasquet also made the grade, following his 7-5, 5-7, 6-3 win over Canada's Frank Dancevic.

Top seed Novak Djokovic of Serbia qualified for the quarterfinals on Wednesday.