Phelps and Lochte seek to land early blows in pool's ultimate contest

America's arch-rivals go head to head tonight in battle for the first medal in the Aquatics Centre

This is box office. More than 100,000 people turned up for the US trials last month; they were there for one reason. More than 50 camera crews turned up for the first US swimming press conference on Thursday; they were there for one reason.

Click HERE to view 'Tale of the tape: Phelps v Lochte' graphic

Tonight at 7.30, the race for the first medal in the London Aquatics Centre will begin, and in what is the least coincidental piece of scheduling since the serpent was dispatched into the garden of Eden with a fancy for a Granny Smith, the reason for that focus will become clear.

It is Michael Phelps against Ryan Lochte, seconds out, round one. It is the greatest duel the pool has seen and it is one that will be settled with a difference of less than a second. At the US trials they raced each other four times and Phelps came out ahead in three of them – his combined margin of victory was three-tenths of a second.

Phelps is, whatever happens in London, the greatest swimmer the world has seen. That is not open to debate, no matter what Lochte achieves over the next week. Phelps will not go home empty handed – there will be more medals to add to the 14 gold, eight from Beijing, six from Athens, and two bronze, both from Athens. At the very least expect three more golds, a return that will make him the most heavily decorated Olympian.

There will probably, in fact almost certainly, be more but it is the battle with Lochte, a man he used to never lose to, that will define his Games. Phelps will swim twice against Lochte, first today in the 400m individual medley and then on Wednesday in the 200m version of the multi-stroke discipline.

Phelps won both in Beijing; Phelps took bronze each time. The man who took silver in each, the Hungarian Laszlo Cseh, will be back too and is capable of getting between the Americans again, but then that would ruin the ending to a script that has been thrillingly written since Beijing.

After Phelps clambered out of the pool following victory in the 400m individual medley, he vowed he would never swim the event again. Lochte finished four and a half seconds adrift of his compatriot and he climbed out of the pool vowing it would be different in four years' time.

What Lochte has done is engineer a remarkable transformation in his fortunes and it has come about through one thing only; a change in attitude. Lochte, a relaxed, easy-going character out of the pool, has undergone an immense, intense training regime and its effect has been to close the gap on Phelps.

At last year's World Championships in Shanghai, it was the 27-year-old Lochte who was the swimmer of the meet. He took four indiv idual golds to Phelps's two – and the difference was two Lochte wins in the individual medleys. There is now little between the two, from the three months that separate their birth dates to, as the US trials showed, their split times in the pool.

But Phelps is an Olympic specialist, a man who thrives on a four-year cycle and there is reason to suppose he will do so again.