After two days off since the sensational gold on 100 meters freestyle, Sjöström was back on half the distance where she is a major favorite.
A fully packed Paris La Défense Arena saw her dominate the heats completely.
She was the only swimmer under 24 seconds and the clock stopped at 23.85 already.
The nearest competitor, Polish Katarzyna Wasick, was beaten by 42 hundredths.
There was a difference of over half a second to third-placed Gretchen Walsh, USA.
Very good, I don't think I've done such a fast heat swim on 50 freestyle at a championship before, says Sjöström.
"Nice to let loose"
A relaxed Swedish described the feeling:
I've been waiting for this, so nice to let loose, says she.
She has enjoyed the reactions on social media after the gold on Wednesday evening.
It's been very nice. I always get very nice support, but this time there have been many who have cheered me on. Even swimmers from nations I competed against. Girls and boys from Australia and USA, coaches, it's very fun, says Sjöström.
Her heat time was only 24 hundredths above her own world record from last year.
The world record in danger
Record pace in tonight's semifinal (at 20.39)?
I'm not going to force anything, I'll just let the swimming come naturally. I'd like to be a little faster than this morning, says she.
Michelle Coleman also advanced to the semifinal and had the seventh time with 24.55.
Very nice. It feels good, there's a little more to take. I was nervous and it feels good, you want to be, you feel like you're getting going again, says Coleman, who was only 29 hundredths above her personal best.
