STOCKHOLM (AFP) - American Jeremy Wariner warmed up for this month's world championships in Japan by running the sixth best ever time over 400m at the Stockholm Super Grand Prix here on Tuesday.

The 23-year-old defending Olympic and world champion, who has said he is aiming to better Michael Johnson's world record of 43.18 seconds set in the 1999 worlds in Seville, won in 43.50sec.

Wariner looked comfortable throughout the one-lap race on a fast track in warm conditions and produced a trademark strong finish to kill off his rivals.

Only Johnson and Harry Reynolds have run faster, while Quincey Watts has also timed 43.50sec.

"My race was pretty much perfect," Wariner said. "My third 100m was a little slow, but I made up for it during my home stretch."

Wariner, who was followed to the line by American duo Kerron Clement (44.48sec) and Darold Williamson (44.90sec), said that an attempt on Johnson's world record in Osaka was not out of the question.

"There's a chance, the track is real fast," he said. "I am not going to force it, I'll just go out there and run my race."

In the men's 100m, Jamaican world record holder Asafa Powell struggled to reproduce his early-season form, just pipping Derrick Atkins of the Bahamas at the line to win in 10.04sec.

"I did not feel so good today, so I did not push it as hard as I should have," Powell said after his last race before the world championships which kick off on August 25.

European champion Susanna Kallur scored a psychological point over defending world champion Michelle Perry in the 100m hurdles, leading throughout in an aggressive showing that saw her home in 12.66sec.

And Croatian high jumper Blanka Vlasic posted her world credentials with a third-best ever jump of 2.07 metres. Her three attempts on the 19-year-old world record of 2.09m held by Bulgarian Stefka Kostadinova narrowly failed.

American Sanya Richards saw her imperious record over 400m falter after she earlier posted an impressive 11.05sec in the 100m and was nipped in a photo-finish over the one-lap race by compatriot Allyson Felix.