Saif Saaeed Shaheen won the 3,000m steeplechase final to give Qatar their first ever World
Championships medal on Tuesday.
The 20-year-old, who formerly ran for Kenya as Stephen Cherono, will earn a $1m bonus for winning gold and is reportedly being paid $1,000 a month to run for Qatar.
Shaheen was engaged in a thrilling battle for the line with former Kenya team-mate Ezekiel Kemboi .
Spain's Eliseo Martin also put in a determined performance to pick up the bronze medal.
Shaheen set off at a lightning pace, covering the first third of the race in world record pace, but he could not sustain it and Kemboi was able to catch him.
It looked as though both athletes had run themselves into the ground as the chasing pack began to close them down.
But the duo kicked again on the final lap to take an absorbing head-to-head battle down to the wire.
Kemboi held the lead until Shaheen delivered a final spurt to cross the line in eight minutes, 04.39 seconds.
"I ran the first 2000 metres very fast," said Shaheen.
"I knew that at that point I could win the race. I let Kemboi catch up with me just to prove that I could beat him."
Shaheen's switch of allegiance ends a run of success for Kenya in the event which stretches back to the 1987 World Championships.