The Americans got the best of their Jamaican rivals in the sprints at the season-opening Diamond League meet in Doha on Friday while the Kenyans outclassed the Ethiopians in the longer distances.
Justin Gatlin led the way for the Americans, nipping Jamaica's Asafa Powell at the line to win the 100 meters in a time of 9.87 seconds.
Allyson Felix then set a meet record in beating Jamaica rival Veronica Campbell-Brown in the women's 100. Walter Dix also set a meet record in the 200 and Olympic champion LaShawn Merritt, who completed a 21-month doping suspension last year, set a meet record and world-leading time this season in easily winning the 400.
Powell got off to the faster start but Gatlin pulled even and then managed to get in front as they crossed the line.
Gatlin tied Powell's world record in Doha six years ago only to see the result erased when he was caught doping a few weeks later. Gatlin had tested positive for excessive levels of testosterone, which led to a four-year ban.
"This is fastest I ever opened up my career," said world indoor champion Gatlin as he dedicated the win to his son Jace, who turned two on Friday.
"I just showed I have a lot of grit and a lot of competition in these old legs. I want to come back and show the world I can run to the line with the best of them."
Powell, who has lost to Gatlin seven times in 10 meetings, said he wouldn't let it happen the next time.
"I cannot complain about my time - 9.88 is a good time," he said. "I am still feeling the jet lag so I cannot say I was 100 percent ready ... I will surely go for gold at the Olympics."
Looking for one last shot at gold at the London Olympics, the 2004 Olympic gold medalist Gatlin said his win was a reminder to Olympic champion Usain Bolt and the rest of the Jamaican team that the Americans would be a force to reckon with in London.
"Everyone wants to see a great competition," Gatlin said of the rivalry. "They have has watched the Bolt show for a couple of years and they want to see someone else in the mix as well. I'm glad to come up and step up and take charge with that."
Bolt skipped the meet, as did Tyson Gay of the United States who is recovering from injury.
Felix, who is considering running the 200 and 400 meters at the London Games, showed her speed work is paying off.
She won the 100 in a time of 10.92, upsetting Campbell-Brown who finished just .02 seconds behind. Olympic champion Shelly-Ann Fraser-Pryce was third, a further .06 seconds back.
"It was very good to get one over Campbell especially at the 100," said Felix, who had never beaten Campbell-Brown in the 100. "It's pretty cool. Jamaicans have some really good racers and the rivalry is good."
Campbell-Brown only said she "could improve" and would "keep working until the Olympics."
The only bright spot for Jamaica was Melaine Walker leading a 1-2 Jamaican finish in the 400 hurdles and Brigitte Ann Foster-Hylton holding off Kellie Wells of the United States in the 100 hurdles.
In the longer distances, Kenya runners dominated their rivals from Ethiopia like they did at the world championships with several setting world-leading marks this season ahead of the London Olympics.
World champion David Rudisha led a Kenyan 1-2 in the 800 by running 1:43.10, .33 ahead of Job Kinyor. The field didn't include main rival Mohammed Aman of Ethiopia.
"1:43.10 is a very good time for me," Rudisha said. "I know that the athletes want to beat me now but I am well prepared to face the challenge. Great 800 meter runners like Coe failed to win an Olympic gold but I will do my best to make it."
Olympic champion Pamela Jelimo also showed her world indoor title in March was no fluke, winning the women's 800 in 1:56.94. Fellow Kenyan and main rival Janeth Jepkosgei finished third.
Silas Kiplagat led a Kenya 1-2-3 in the 1,500, in a time of 3:29.63.
In the 3,000, two-time world champion Vivian Jepkemoi pulled away in the final 200 meters and then held off Meseret Defar of Ethiopia to win in 8:46.44. It is only the second time Jepkemoi has beaten Defar, who has set 13 world records and won 16 global titles.
Jepkemoi she almost skipped the meet because her left ankle had been bothering her.
"You see the way I closed it up because no one wanted to go," said Jepkemoi, who expects to go for a double in the 5,000 and 10,000 at the Olympics. "I'm happy because I won. I said let me try my best. If you have an injury, you can't imagine you would win."
In the final race, Augustine Chogeled led a Kenyan 1-2 in the 10,000 as Ethiopian great Kenenisa Bekele finished 10 seconds behind in seventh place. The poor showing raises doubts about Bekele'd bid to come back from a string of injuries and compete in the 5,000 and 10,000 in London.
"I missed one week training a little bit my Achilles was not good," Bekele said. "Because of that, I took two or three days rest ... So sorry."