Great Britain's Mo Farah finished third in his 5,000m heat to automatically qualify for the final and stay in contention for double Olympic gold.
won the 10,000m on Saturday
and was given a huge roar from the crowd when introduced at the start line.
He had to work to book a spot in a second final, admitting: "It was pretty difficult as I was tired."
"Mo had to work hard. Even for Olympic champions 12-and-a-half laps can still be hard work. Mo is going to have to be absolutely at his best to win gold. When he gets to the final, he'll want to be controlling it rather than reacting to it."
Fellow Briton Nick McCormick was 12th in heat two and failed to reach Saturday's final.
Farah stuck around after his third place to watch the second heat to study his rivals as he bids to add an Olympic gold to his World crown in the 5,000m.
"The heat took a bit more out of me than I was expecting," he added. "But I'm really happy with where I am now and I've got a couple of days off.
"I kept getting caught as there was a lot of pushing and shoving going on. That's what happens in the heats. Hopefully, it will settle down in the final."
McCormick ran in the faster heat and narrowly missed out on a final spot as a fastest loser.
"I did everything I possibly could," he said. "I'm disappointed I missed out by two spots, but it was a brilliant occasion.
"I loved the crowd, they were absolutely fantastic. I gave it everything, but I have come a long way from where I was two years ago and I'm just disappointed not to make the final.
"I think I could have done. It was a very scrappy race. I just didn't have enough but I gave it everything, I've got no regrets."