Tanui, who finished third in the 10,000m at the 2013 and 2015 World Championships, was elated to make the cut for Rio after his win, which was watched by an unusually large crowd at the Kipchoge Keino Stadium.
"I am so happy because although I knew I would run well, I did not expect to win and be in the Olympic team," said the 25-year-old, who won in 27 minutes 46.15 seconds ahead of second-placed Charles Yossei.
"It is a pleasant surprise to be in the Olympic team, which has always been my dream."
Kamworor and Karoki started the race at a searing pace, intermittently exchanging the lead, and it was the 25-year-old Japan-based Karoki who dropped out first in the 10th lap, complaining of body aches.
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Kamworor, who won the half-marathon races in Cardiff, Lille and Berlin, stayed in lead with Japan-based Tanui and William Malel Sitonik, but with four laps left, he dropped out too.
"I suffered stomach cramps and could not just go through," said Kamworor.
The 24-year-old Kamworor was in line to get a wild card for the 10,000m team, but has clouded his chances after a row.
"We had slotted him for a wild card, but he insisted on a written commitment, which we don't do," said one of the selectors, who did not wish to be named.
Yokes Ondieki, who won the 10,000m race at the 1991 World Championships in Tokyo, said foreign-based athletes need time to acclimatize for such events.
"You don't fly in from abroad and expect to do well in such altitude and climate. Many factors need to be fine tuned, like food etc," Ondieki said.
(Editing by Sudipto Ganguly)
