LaShawn Merritt ran the race of his life when it mattered most to defeat defending Olympic and two-time world champion Jeremy Wariner in a 400-meter final showdown yesterday that ended with a U.S. sweep. Merritt, the 2007 world runner-up to Wariner, won in 43.75 seconds, a lifetime best that only four runners in history have ever bettered. Wariner was a stunned second in 44.74 with David Neville completing the U.S. haul in 44.80. The best prior time for Merritt was 43.96 from his loss to Wariner in last year's worlds.