Felix, who eased to victory in the 200 on Friday, became the first athlete to win double maximum points in a Diamond League meeting and is considering running both events at next year's world championships and the 2012 London Olympics.
"I really hope so," Felix said when asked about doing the double in a trackside interview "I'm going to work really hard and we'll see." But the American found the going tough over the longer event in front of a packed Crystal Palace on a breezy, overcast day. After going off quickly, she came under pressure from Russia's European champion Tatyana Firova and world indoor gold medallist Debbie Dunn in the home straight.
However, the triple world 200 champion held her form to win in 50.79 seconds. Firova was second in 50.84 and Dunn third 0.05 behind.
"It was a tight race and I really had to rely on my endurance," said Felix who also won the 400 at the Doha and Eugene Diamond League races.
"The time wasn't great but it wasn't about the time today, it was a great field and I just wanted to execute my race. It was more difficult than yesterday's race... so I was happy to pull that one off." Felix's compatriot Christian Cantwell had a less happy time at Crystal Palace when the world shot put champion suffered his first defeat in 21 meetings.
Cantwell struggled from the start, opening with a no-throw, but pulled off 20.78 on his final attempt for third behind fellow American Reese Hoffa, who threw 21.44 and Poland's Tomasz Majewski on 21.20.
"I really don't know what was wrong. I was just a wuss, I guess," said the 29-year-old Cantwell. "I have no excuses, no niggles or anything. It was just a bad day."
There was also a surprise defeat for Carmelita Jeter in the women's 100 final when she finished second to fellow American Marshevet Myers in a tight race.
Myers, who clocked 10.99 in her heat, held off the favorite to win in 11.01 for her first Diamond League victory. Jeter was second in 11.06.
American David Oliver maintained his unbeaten record outdoors this year with a convincing win in the 110 hurdles. The 28-year-old led from the first barrier and equalled Briton Colin Jackson's meeting record of 13.06.
Wallace Spearmon, who was seventh behind Tyson Gay in Friday's 100 meters final, was back on more familiar ground when he won the 200.
The American world championship bronze medallist ran a good bend and powered away in the final 40 meters for a clear victory in 20.12.
His compatriot Jeremy Wariner notched his fifth Diamond League victory over 400 holding off fast-finishing Jamaican Jermaine Gonzales, the quickest man in the world this year, to win in 44.67.
"Jermaine came into this meet with the world's fastest time, and I was able to run my race and come out on top. After all my injury problems I am really pleased with how today went," said the former world champion, who had a knee problem earlier this year.
