Olympic Games, London, Day 5 semi-finals
Men's 200m medley
In the blue corner, Michael Phelps, greatest of greats, in the red corner, Ryan Lochte, the swimming rock star who has helped it rain on his fellow American's parade at these swansong Games in London.
The sensational sixth-day showdown between the towering teammates dawns.
Lochte, 28, has the bigger job: at about 8pm, he will take to the water to defend his 200m backstroke crown, take a breather while a women's semi-final unfolds, and then return to the fray to face Phelps in the 200m medley, the race that decides the best all rounder the last in which the two will ever join in battle.
Phelps, 27, will leave the race with two more in him, the 100m butterfly and then the 4x100m medley on the last day of his racing life on Saturday before hanging up his golden goggles with what is likely to be 22 medals, four more than the next best and at least 15 of them gold, six more than the next best.
This week has set a punishing pace for both men, relatively late finals dictating that when Lochte left the water after winning the 400m medley last Saturday to run the gauntlet of media and doping control before dinner, he would not get to bed until 2am. He was up before 8am preparing for the next wave of challenge in a seven-event programme.
Lochte now faces Phelps at his most vulnerable, a man locked out of the medals in the 400m medley, denied his dream of the triple crown in his signature event, the 200m butterfly, by Chad Le Clos, a 20-year-old South African 0.05sec ahead of him. Rivals have smelled blood from the moment Phelps found himself in a shadowy place he'd never been before in Olympic waters: 4th.
Still, caution is urged when dealing with the great white of the race pool, who knows he is taking on a kindred spirit today but a man who will still be panting from the 200m backstroke final when he arrives at his blocks for the medley.
He was third fastest through semis in 1:57.11, Lochte well ahead of him in the first semi, on 1:56.13. The two Americans then watched to see what Laszlo Cseh, of Hungary, had: 1:56.74 in the second semi.
The podium placers of 2008 are back for one more battle, arguably the three greatest all rounders in swimming history.
Canada's Andrew Ford finished outside the final - placing 15th in 2:01.58.