Filip Ingebrigtsen, a world championship bronze medallist in 2017, was disqualified from his 1,500m heat for straying off the inside of the track after he tried to squeeze through a gap that wasn't really there.
Jakob Ingebrigtsen, a double European champion outdoors in Berlin last year, looked comfortable in winning his heat, as did the defending champion, Poland's Marcin Lewandowski.
The 19-year-old Norwegian was back on the track 90 minutes later as he safely advanced from the 3,000m heats, with the final on Saturday night when his other brother Henrik, will also be on the start line after qualifying safely despite a lot of pushing and bumping in his heat that left him bleeding.
"I feel pretty strong, have done a lot of mileage to prepare for this," Jakob Ingebrigtsen, who was unimpressed by his brother's disqualification in the earlier event, told the BBC.
It was the stupidest thing I'll see all year. I saw the race and there was nothing wrong with it. I believe it's the new tactics for the 1,500 - you push someone and you qualify.
Belgium's Ismael Debjani was also disqualified for the same offence after initially going through in the 1,500m.
In the absence of Belgium's dominant Nafissatou Thiam, Britain's Katarina Johnson-Thompson was on course for the pentathlon title after solid performances in the three morning events - the 60 metres hurdles, high jump and shot.

Johnson-Thompson finishes second to Solene Ndama in pentathlon hurdles

The remaining events take place in Friday's evening session, which also features the women's 3,000m final.