The defending Olympic champion broke the Drake Relays record with a world-leading time of 44.08 seconds Friday.
James, who represents Grenda, beat American LaShawn Merritt by 0.14 seconds and shaved over a quarter of a second off the time he posted at a race in the Bahamas two weeks ago.
The performance only solidified James' status as the early favorite in the 400 for the Rio Olympics this August. His time nearly matched the 43.94 he ran to win in London -- and James still has three months to prepare for Brazil.
The time James posted was even more remarkable given the conditions, with temperatures hovering just below 50 degrees. The conditions got to Merritt, the 2008 Beijing Olympics champion. He finished 2015 ranked second in the world and is hoping to be ready to push James by the Rio Games.
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"I wanted to win the race. But I didn't want to kill myself," said Merritt, who matched the old meet record. "My toes felt frozen. So when I tried to like really push at certain parts, I felt like I was just tip-toeing. But I finished up healthy."
It was a promising early run for Jackson, who is hoping to overcome personal tragedy and gain a measure of redemption after barely missing out on a spot on the U.S. Team in the London Olympics four years ago.
Jackson overcame a struggle on the ninth hurdle to beat Michael Tinsley, the silver medalist in London, in his outdoor season debut.
"This season right here, 2016, is going to define Batman's legacy," Jackson said. "Sometimes I defeat myself. But coming into this race, I didn't know where I was...I had mixed emotions. But one thing about me. I'm a competitor."
Lorraine Ugen upset London Olympics champion Brittney Reese, winning at 22 feet, 4 1/2 inches.
Reese was fighting an injury to her left ankle that she had to tape up, but she didn't blame the setback on her performance. Reese's best jump fell three inches shy of Ugen's mark.
"Actually I wasn't disappointed. I was consistent the whole time," Reese said.
Canadian Shawn Barber won the men's pole vault in 18 feet, 1/2 inches, and Derek Drouin took the men's high jump at 7-4 1/4.