It was at last summer's US Open that Andy Roddick upset Novak Djokovic with comments about his illness and injury record. Asked which ankle Djokovic had injured in his previous match, Roddick replied: "Isn't it both of them? And a back and a hip? And a cramp, bird flu, anthrax, SARS, a common cough and cold." Djokovic, who responded by beating Roddick and then upsetting the crowd by criticising the local hero for his remarks, played him again here yesterday at the Australian Open. The outcome? Djokovic retired with "heat illness" when trailing 6-7, 6-4, 6-2, 2-1 to send Roddick through to the semi-finals, where the American will renew his rivalry with Roger Federer, who needed only 80 minutes to beat Juan Martin del Potro 6-3, 6-0, 6-0.
The front page headline of yesterday's Herald Sun screamed: "Heat wave hell." Weather forecasters here are predicting five consecutive days above 40C for the first time since 1908.
Tournament organisers can stop matches if their "heat stress index" – which usually means temperatures above 38C – reaches a certain level. By the time Djokovic quit two and a half hours into the match the air temperature topped 37C; on the court itself it is generally reckoned to be 10 degrees hotter. The sun has been ferocious this week, with courtside photographers covering themselves with towels after complaining of getting burned through their clothes.
To add to Djokovic's problems the defending champion had only 36 hours to recover from his previous match, which finished at 2.26am on Monday. The world No 3 got to bed at 6am and felt too tired to practise that day. His request for another night match fell on deaf ears.
Unfortunately for the 21-year-old Serb, he has earned a reputation as a sick-note specialist. This was his fourth retirement in only his 17th Grand Slam tournament. In contrast, Federer, Rafael Nadal and Andy Murray have never retired from a Grand Slam match; indeed Federer has never quit in 775 matches as a senior professional.
Djokovic, who looked in trouble from the second set onwards, said he had retired because of "cramping and soreness in the whole body". He insisted: "I've had some retirements, but I've always retired with a reason and because I felt I could not go on. Today I really tried my best but sometimes you can't fight against your own body."
After the third game of the third set Djokovic took a three-minute medical time-out to receive a massage. The abuse of medical time-outs – some players clearly use them to break their opponent's concentration – has become an issue and the break affected Roddick's rhythm. In the next game he served three double faults.
Roddick, who agrees with a suggestion that time-outs for cramping should be allowed only before a player's own serve, added: "I looked over [at Djokovic] and I was confused, because I thought it was one injury per time-out and I saw a calf, a neck, and an arm. But I guess cramping is one condition."'
Did Roddick feel there was a question mark over Djokovic's durability? "He's got through tough matches. Today just wasn't his day physically, I guess." However, the American had sympathy with Djokovic over his late-night finish, having regularly suffered the same fate at the US Open.
Broadcasters might not like it, but they may soon come under pressure to accept evening sessions consisting of one singles followed by a doubles rather than two singles matches.
Roddick was pleased that he had ended on a positive note by breaking Djokovic's serve in the final game.
He has enjoyed a fresh lease of life working with Larry Stefanki and is looking leaner and meaner than he has for several seasons.
"Getting in better shape was his impetus," Roddick said of his new coach. "I think we have similar minds. We both like going to work and have a lot of the same interests. We're on a par as far as our energy levels are concerned. We don't like sitting around being bored. It's been really good so far."
Roddick has lost 15 of his 17 matches against Federer, though he won when they last met in Miami 10 months ago, when the Swiss was recovering from the glandular fever that ruined his chances at last year's Australian Open.
With the exception of his five-set struggle against Tomas Berdych, Federer is looking in great shape this time around. He was back to his majestic best against Del Potro, conceding just 14 points in the last two sets against one of the game's rising talents. In the last six months Del Potro has climbed 59 places to No 6 in the world rankings.
Jelena Dokic's fairytale run ended when the world No 187 was beaten 6-4, 4-6, 6-4 by Dinara Safina, the world No 3, in the first match of the evening session. In the semi-finals Safina will play her fellow Russian, Vera Zvonareva, who beat Marion Bartoli 6-3, 6-0 in the heat of the day after losing three of the first four games. While Zvonareva was at the top of her game, Bartoli suffered in the heat. "It was really hot," she said. "I don't think it's really fair to have one quarter-final played at 1pm, right in the middle of the heat, and one playing at 7.30pm."
Jamie Murray followed his brother Andy out of the tournament when Andy Ram and Nathalie Dechy beat the Scot and his partner, Liezel Huber, 6-7, 6-2, 10-4 in the mixed doubles. Britain's Laura Robson and Heather Watson continued their progress in the junior singles, both moving into the third round with straight-sets victories.
The retiring world No 3
Djokovic has played in 17 Grand Slam tournaments and retired during four of them:
2005 French Open second round - Retired with lower back injury when trailing Guillermo Coria 6-4, 2-6, 2-3.
2006 French Open quarter-final - Retired with breathing difficulties after losing first two sets to Rafael Nadal.
2007 Wimbledon semi-final - Retired with infected blister against Nadal when losing 6-3, 1-6, 1-4.
2009 Australian Open quarter-final - Retired after suffering from "heat illness" when trailing 7-6, 4-6, 2-6, 1-2 to Andy Roddick.