MELBOURNE, Australia -- No. 21-seeded Philipp Kohlschreiber, followed by No. 13 John Isner, were among five players who dropped out of the Australian Open on Tuesday, joining No. 12 seed Tommy Haas and two other players who withdrew Monday.
Despite temperatures reaching 108 Fahrenheit during the afternoon and a hot breeze gusting over Melbourne Park for most of the day, none of the withdrawals were apparently linked to the oppressive heat.
Germany's Kohlschreiber withdrew with a strained left hamstring before his scheduled first-round match against Slovenian Aljaz Bedene.
He was replaced in the draw by Frenchman Stephane Robert, a lucky loser from qualifying who beat Bedene 7-6 (3), 6-3, 6-0.
Isner then retired from his match against Slovakia's Martin Klizan with a lingering ankle injury that he said got progressively worse at the Hopman Cup event in Perth and a tournament he won in Auckland, New Zealand, over the past two weeks.
Czech veteran Radek Stepanek later 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 worse throughout the match.
German Julian Reister also 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.
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 on court for only 10 minutes, collected $27,000 for losing in the first round, or $2,700 per minute.
A few other players struggled in the heat 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."
The Associated Press contributed to this report.