The other seeded player in his section of the draw, Philipp Kohlschreiber of Germany, withdrew before his scheduled first-round match against Slovenian Aljaz Bedene with a left hamstring injury.
He was replaced in the draw by Frenchman Stephane Robert, a lucky loser from qualifying, who defeated Bedene to reach the second round.
Hometown favorite Bernard Tomic later retired with a left leg injury after losing the first set against top-seeded Rafael Nadal 6-4, much to the astonishment of the Rod Laver Arena crowd, who initially booed him.
"It was very difficult for me to say sorry to the crowd," he said. "I don't think they quite knew what was wrong with me."
Czech veteran Radek Stepanek also retired from his match against Slovenian Blaz Kavcic with a neck injury while leading 7-6 (3), 6-4, 1-6, 0-2 after nearly three hours of play.
He said the problem started in the first set and got progressively worst throughout the match.
And German Julian Reister quit while trailing Brazilian qualifier Thomaz Bellucci 4-6, 6-3, 7-6 (5). A reason for his withdrawal was not immediately given by tournament officials.
A few other players struggled in the heat on Tuesday, but finished their matches. Canadian qualifier Frank Dancevic said he blacked out during his 7-6 (12), 6-3, 6-4 loss to No. 27-seeded Benoit Paire of France.
Dancevic, who required medical attention during the second set, questioned the wisdom of not suspending matches during the torridly hot conditions.
"I don't think it's fair to anybody, to the players, to the fans, to the sport when you see players pulling out of matches and passing out," he said. ""I think it's definitely hazardous to be out there. It's dangerous."
On the women's side, Polona Hercog of Slovenia retired with a shoulder injury after losing the first game of her match against 25th-seeded Alize Cornet of France.
Hercog, who was only on court for 10 minutes, collected 30,000 Australian dollars ($27,000) for losing in the first round, or AU$3,000 ($2,700) per minute.
