I thought I was better placed, says Peirsol

Aaron Peirsol's shot at a fourth straight 100m backstroke world title evaporated Monday with a 'huge miscalculation' that cost him a spot in the World Championship final.

Less than three weeks after he set the 100m backstroke world record with a time of 51.94 at the US trials, Peirsol failed to reach the World Championship final.

The defeat means he won't get a chance to add to the 100m titles he won in 2003, 2005 and 2007, which go with his Olympic golds from 2004 and 2008.

"That was a huge miscalculation," Peirsol said. "I thought I was in a much better place in that race than I was."

Peirsol finished fourth in his heat, won by Aschwin Wildeboer Faber, a Spaniard who had seized the 100m back world mark for a week in July before Peirsol grabbed it back.

"I thought I was right next to Ashwin, I didn't know I was half a second behind," said Peirsol. "It was very strange to see that time. Usually I'm not that bad (at judging his pace)."