Injury-hit Ingebrigtsen fails to advance in world 1,500m
Ingebrigtsen, who won Olympic 1,500m gold in the Japanese capital in 2021 but was searching for a first world title over the distance, has been laid low with an achilles injury that has seen him miss all of the outdoor season.
In his heat at the National Stadium, things seemed as normal as Ingebrigtsen fell into his usual spot at the back of the pack.
But coming into the final lap, the 24-year-old was boxed in on the inside with seemingly little room to manoeuvre.
As it was, Ingebrigtsen had nothing to offer acceleration-wise and eventually finished eighth in a heat won by Britain's Jake Wightman.
Only the top six from each of the four heats qualify for Monday's semi-finals, with the final set for Wednesday.
"It's a first-time experience that I haven't got to the next round," said Ingebrigtsen.
"Of course, it's very disappointing but at the same time it is a reality check."
Ingebrigtsen added: "This is an event that's very competitive. You need to prepare your best and of course, I'm not there."
The question now is whether Ingebrigtsen, who picked up his injury after completing a rare world indoor double over 1,500m and 3,000m in Nanjing in March, bids for a third world title in the 5,000m, with heats scheduled for Friday and final on Sunday.
But the Norwegian remained as optimistic as he could in the immediate wake of such a disappointing outing.
"I think I'm probably closer for the 5,000m race right now," he maintained.
"I'll recover and have a couple of good days until I go again (in the 5,000m heats) and try again. Everything is a test. I was trying to do my best to advance to the semi-final but it was terrible.
"You have to start and you have to try."
'Big step'
Wightman and compatriot Josh Kerr have dashed Ingebrigtsen's title hopes in the past two world championships over 1,500m in Eugene and Budapest.
"I am coming here as someone who's done it before and I am coming to do it again," said a confident Kerr of his ambitions.
"I am here to win, but it does not come from one race. I want to stay present in what I am doing and work hard."
Olympic champion Cole Hocker led a cohort of US teammates successfully through the heats, notably Jonah Koech, who recovered from a fall to sprint back into one of the qualifying spots.
Wightman, with Neil Gourlay a third Scot also going through to the semis for Britain, added: "The goal was to get through to the next round.
"That was a big step for me having not been to the world championships for three years. It's nice to be down on the track rather than being in the stands.
"I'm not putting too many expectations on myself. Hopefully, when it comes to the final I can put all my energy towards it."