The Ulsteinvik man clocked in at 45.86 in the second heat in Glasgow. It lasted until a clear victory ahead of the Jamaican Rusheen McDonald.
The three best times in each semi-final pool granted advancement.
– It may look like we will have a duel between Norway and Belgium in the final. Alexander Doom is no bad finisher either, said NRK’s athletics expert Vebjørn Rodal after the finish.
Doom was fastest in the first semi-final when he set the best record with a time of 45.69.
Earlier on Friday, Warholm easily won his trial heat in 46.68. Sunnmøringen has 45.05 as her personal best in the 400 meters indoors.
It is the first time that Warholm competes in an indoor WC.
– No one gives this a very high priority. This means that there are opportunities for everyone to take scalps. I am doing this to be better prepared for the summer, Warholm said at Thursday’s press conference.
Read also: Guide: This is what you need to know about the Athletics World Championships in Glasgow