David Rudisha never doubted his ability to win the men's 800 metres after going back-to-back at the Rio Olympics.
The Kenyan produced another majestic performance to beat Algerian Taoufik Makhloufi and American Clayton Murphy on Monday.
Rudisha became the first man since New Zealander Peter Snell in 1964 to defend the 800m crown.
The 27-year-old, now a two-time Olympic champion, said he was always confident after winning in a time of one minute and 42.15 seconds.
"Running 1:42, it's just fantastic. I had no doubts before. The feeling in my body was good," Rudisha said.
"It is great to win such a big competition, my second gold. It's so great. I am so excited. It is the greatest moment of my career."
Rudisha, who missed the 2013 world championships due to a knee issue, said it had been tough to overcome his injuries.
"It's been very difficult. I have stayed focused and positive," he said.
"My coach has been great and given me hope. I dedicate this medal to God."