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Head to head: Five duels that will define the 2012 games...

1. Usain Bolt v Yohan Blake (100m and 200m sprints)

The fastest man the world has seen -- the greatest title in sport -- against the man who would be king. The line-up for both races will almost certainly be the quickest ever seen on earth, but it is the duel between the two Jamaicans that may well come to define London 2012. Bolt is the one with it all to lose. The defending 100m and 200m champion and world record holder in both has shown signs of being human after all since his stunningly brilliant double triumph in Beijing. He is not the form runner: that is Blake, his younger training partner. The 22-year-old, the youngest man to run inside 10 seconds and the youngest-ever world 100m champion, beat Bolt twice in the Jamaican trials.

2. Michael Phelps v Ryan Lochte (Swimming events)

Another quest to depose the king. Phelps is the greatest Olympian the pool has ever seen and will remain so whatever happens in London -- from where he certainly will not return empty handed. What is also certain is that he will not match his phenomenal deeds of Beijing -- where he claimed eight gold medals -- to add to the six from Athens. He is only -- only -- going for seven this time, but in his way is the late-blooming Lochte. The 27-year-old already has three Olympic golds to his name and will be competing in a third Games. Honours finished just about even in the US trials but the Olympics is all about peaking at the right moment and that is what Phelps is extraordinarily adept at.

3. Mark Cavendish v Peter Sagan (Men's road race)

This may not reach the heights of Bolt v Blake or Phelps v Lochte, but it is a duel that could determine the direction the Games take for a medal-hungry home nation. The men's road race will hurtle around Surrey and then down the Mall mid-afternoon on the first day of the Games. If all goes according to plan it will deliver a first gold of the London Olympics for Britain. Cavendish famously came back from Beijing as the only member of the track team not to win a medal. This time he is on the road and an Olympic gold is his priority. Sagan and his Slovakian team are his likeliest challengers. The 22-year-old impressed in his debut Tour -- Dave Brailsford, the Team Sky principal, compared watching Sagan to seeing Lionel Messi play football.

4. Katie Taylor v Natasha Jonas (Women's Lightweight Boxing)

Taylor is the undisputed Queen of women's boxing. Four times world champion and five times European champion, the Bray native is the shining light of the sport and a huge factor in its inclusion in this Olympiad. Like Taylor, 28-year-old Jonas was an accomplished soccer player that chose to concentrate on boxing. A bronze-medallist in this year's World Championships, the Liverpudlian has claimed in the run-up to the games that she gave Taylor too much respect when the Irishwoman beat her 6-3 last year and revealed that she has been studying Ireland's leading gold medal contender. Buoyed by home support Jonas could be Katie Taylor's leading rival for OIympic gold.

5 China v United States

(To top the medal table)

The contest to top the medal table is unsurprisingly a two-horse race. In Beijing the US collected 107 medals, China 100 and next best was Russia a distant third with 73. It was China who topped the table with their haul of 51 gold medals -- a comfortable margin clear of the US, who collected 36. Carl Lewis, for one, believes London will prove a home from home for the US, given many athletes' familiarity with the capital and the language and cultural similarities. China's rise to sporting superstardom has been dramatic -- They will take some shifting.