Fresh from his success in Moscow earlier this month, Merritt (44.69 seconds) was slower by nearly a second than his time at the world championships but still won by more than half a second from Dominican Republic's Luguelin Santos.
Compatriot David Oliver, the 110 metres hurdles world champion, also triumphed in his event, while women's 800 metres runner Eunice Sum, women's 400 hurdler Zuzana Hejnova and shot putter Valerie Adams were other successful world champions.
Ethiopian women's 5,000m world and Olympic champion Meseret Defar stormed to victory in the 3,000m to win in 8:30.29, the world's fastest time this year.
"To be able to come and win just a few days after the world championships is good," Defar said on the website of the sport's governing body, the IAAF (www.iaaf.org).
"I am so happy for this victory. I ran 14.50 (for the 5,000m) at the world championships, which is not fast for me, so I was able to run well tonight. I'm in good shape."
The women's high jump event featured eight of the top nine finalists from Moscow and once again Russia's Svetlana Shkolina came out on top to remain unbeaten this season.
Another world champion Russian, men's long jumper Aleksandr Menkov, leapt to victory on a chilly night in Stockholm.
Three women earned one-carat diamonds after setting Olympic Stadium records with Czech Republic's Hejnova running the 400 hurdles in 53.70 seconds, New Zealand's Adams throwing 20.30 metres in the shot put and Russia's Mariya Abakumova setting a mark of 68.59 metres in the javelin.
There was an upset in the men's 1,500m where Kenyan world champion Asbel Kiprop could only finish sixth as Djibouti's Ayanleh Souleiman took the victory in 3:33.59 in a race that was much faster than in Moscow.
- Sports & Recreation
- Zuzana Hejnova
- Valerie Adams