When Novak Djokovic walked off the court after retiring with a sore shoulder in the Cincinnati Masters final against Andy Murray on Sunday he looked so exhausted that you wondered whether he would win another match this year, let alone another title. However, the 24-year-old Serb is one of the game's finest athletes and believes that he can recover in time to resume his one-man assault on the year's major prizes when the US Open begins on Monday.
Despite his second defeat of 2011, Djokovic is still on course to complete one of the greatest seasons in tennis history. The world No 1 cannot win the Grand Slam of the game's four major titles, having lost in the semi-finals of the French Open to Roger Federer in his only other defeat this year, but if he adds the title at Flushing Meadows to his Australian Open and Wimbledon crowns his season will still stand comparison with the best.
Djokovic has already won nine titles this year. Although there are not enough tournaments left in his schedule to beat the record of 17, the quality of his wins has been exceptional.
Beneath the Grand Slam tournaments, the most important competitions are the season-ending World Tour Finals and the nine Masters Series events. Not only has Djokovic become the first player to win five Masters Series titles in a single season – with two still to play – but he has also been competing against two of the greatest players of all time in Federer and Rafael Nadal. In addition he has the chance to lead Serbia to a second successive Davis Cup triumph.
The obvious seasons to compare with Djokovic's are the three years in which male players have won pure Grand Slams. Rod Laver's 1969 season was the most significant in that the Australian was up against all the world's best players; Don Budge in 1938 and Laver in 1962 competed only against amateurs. Laver also won 13 other tournaments in 1969 in addition to his Grand Slam titles.
Jimmy Connors might have emulated Budge and Laver but for his suspension from the French Open in 1974, while only Nadal's victory in the final at Roland Garros prevented Federer from doing the same in 2006 and 2007. Nadal himself won two Grand Slam tournaments and Olympic gold in 2008 and three Grand Slam titles in 2010.
Three women have won the calendar Grand Slam, with Steffi Graf's 1988 "Golden Slam", including the Olympic title, eclipsing the achievements of Maureen Connolly in 1953 and Margaret Smith Court in 1970. Martina Navratilova never won the Grand Slam, but in 1983 she lost only once in 87 matches.
So which might be considered the greatest of all? No player has dominated one year as thoroughly as Navratilova did in 1983, but ultimately the vote would have to go to Graf in 1988, with Laver's 1969 season the greatest among men.
John McEnroe: 1984
McEnroe lost only three times in the year but his first defeat was to haunt him for the rest of his career. The American had won his first 42 matches of the season and appeared to be coasting to victory in the French Open final against Ivan Lendl. However, after winning the first two sets, McEnroe lost his focus and went on to lose the match. It was the closest he came to winning the French Open, the only jewel missing from his Grand Slam crown.
The only other matches McEnroe lost that year were against Vijay Amritraj in Cincinnati and Henrik Sundstrom in the Davis Cup final. The Sundstrom defeat was also on clay – never McEnroe's most productive surface. He chose to play only two other tournaments on clay that year.
Elsewhere, however, McEnroe was all but invincible. He did not compete in the Australian Open but beat Jimmy Connors in the final at Wimbledon and Lendl in the final of the US Open, claiming 13 titles in total in the most successful year of his career.
Roger Federer: 2006
The player acknowledged as the best in history won 11 titles in both 2004 and 2005 and then went one better the following year. Only two players beat him in 2006 – Rafael Nadal, who got the better of him in four finals during an extraordinary run in the spring, and Andy Murray, who beat him in the second round in Cincinnati. The latter was Federer's only defeat between the French Open and the end of the year.
Some of the matches against Nadal were remarkable. With Masters Series finals still played over five sets, Nadal triumphed after nearly four hours in Monte Carlo and more than five in Rome, where Federer had two match points. The French Open and Wimbledon finals both went to four sets.
Federer beat Marcos Baghdatis in the Australian Open final, avenged his Roland Garros defeat against Nadal to win Wimbledon and overcame Andy Roddick to take the US Open. The Swiss won Masters Series titles in Indian Wells, Miami, Toronto and Madrid and rounded off the year by taking the Tennis Masters Cup.
Jimmy Connors: 1974
Connors began by winning his first Grand Slam tournament on New Year's Day, beating Phil Dent in the final of the Australian Open. By the end of the year the fiery American had won 15 tournaments and 95 of his 99 matches. He played every match in the same pair of white shorts, which he washed in his hotel room each night.
Abrasive, outspoken and crude, Connors offended with his behaviour and crushed opponents with his all-action tennis. He went on to win Wimbledon and the US Open (Ken Rosewall took six games off him in the final on Centre Court, four more than he won in the final in New York) but was denied the chance of a Grand Slam when he was banned from the French Open after signing up to play World Team Tennis in events that clashed with the major European tournaments. Connors never played Rod Laver or John Newcombe that year – with different organisations fighting for control of the sport some top players rarely met – but beat Bjorn Borg, the French Open champion, when they met on clay in Indianapolis two months after Roland Garros.
Steffi Graf: 1988
Graf is the only player, male or female, to have won what became known as the "Golden Slam" – victories in all four Grand Slam singles tournaments and the Olympic Games in the same year. Graf won a total of 107 singles titles, including 11 in 1988. As well as the Grand Slam titles and the Seoul Olympics, she won in Miami, San Antonio, Berlin, Hamburg, Mahwah and Brighton.
The German suffered only three defeats all year, to Gabriela Sabatini in the final at Boca Raton and in the semi-finals at Amelia Island and to Pam Shriver in the end-of-year championships. She earned revenge over Sabatini in the finals of the US Open and Olympics and in the semi-finals at Roland Garros.
Graf was only 18 at the start of the season. She had won her first tour title two years earlier. She went on to win her 22nd and last Grand Slam singles crown at the 1999 French Open – only Margaret Smith Court has won more with 24 – before announcing her retirement later that year, while still ranked No 3 in the world.
Rod Laver: 1969
When Laver became only the second man in history (after Don Budge) to win the calendar Grand Slam in 1962, even the Australian himself would have admitted that he was not necessarily the best player in the world. In those days the Grand Slam tournaments were open only to amateurs and not to professionals like Pancho Gonzalez.
In 1968, however, tennis went open and when Laver repeated his Grand Slam feat the following year he did so by winning tournaments that were open to everyone. In total that year the 'Rockhampton Rocket' won 17 singles tournaments – only Guillermo Vilas in 1977 has won as many in a single season – and 106 matches, with 16 defeats.
Tony Roche, a fellow countryman, beat Laver five times that year but lost a marathon five-setter in the semi-finals of the Australian Open. Laver went on to beat Andres Gimeno in the final. His next three Grand Slam titles all came with final victories over fellow Australians: Ken Rosewall in Paris, John Newcombe at Wimbledon and Roche in New York.
Martina Navratilova: 1983
Navratilova was a winning machine. In total the Czech-born player won 167 singles titles and 177 in doubles. She won Wimbledon nine times, claimed an extraordinary 59 Grand Slam titles in singles, doubles and mixed, and won at least one Tour event every season for 21 years in succession. She was world No 1 for 331 weeks.
Never was her domination more emphatic than in 1983, when she won 86 of her 87 matches. Her only defeat was to Kathleen Horvath in the fourth round of the French Open. Chris Evert, Navratilova's perennial rival, lost to her six times in the year, including five finals. Navratilova won Wimbledon and the US Open without losing a set, while Britain's Jo Durie was the only player to take a set off her at the Australian Open.
Navratilova nearly enjoyed as successful a year in 1984. After losing to Hana Mandlikova in the final of her first tournament in Oakland in January, she did not fail again until the last, when she was beaten by Helena Sukova in the semi-finals of the Australian Open in December.