Sjöström recorded 24.62 in the Swim Open at Eriksdalsbadet in Stockholm and was three tenths ahead of multiple Olympic and World Championship medalist Siobhan Haughey of Hong Kong, who swam in the heat after the Swedish star.
Even though it was only a trial - the final will be decided tonight - the stands were packed, and when she was introduced there was loud cheering.
There's usually not this kind of interest around a trial swim; it was a bit of fun, says the swimming star who did her first competitive race in 607 days.
The last time she competed was in Stockholm, just days after her Olympic gold medal success in Paris with double victories in the 50 and 100 meter freestyle.
In August last year, just over seven months ago, she became a mother to Adrian.
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So a new chapter now begins in the 32-year-old's unparalleled swimming history.
For example, the Saturday morning workout wasn't what it usually is before a competition, she notes with a laugh:
It's a little different now with a baby, I played a little, rested, had a coffee. It's going to be a pretty long day, I woke up at 5 a.m., maybe you wouldn't have done that before a competition otherwise.
Sjöström's time was surprisingly good - 24.62 is the seventh fastest time in the world this year, in a trial session after 20 months away from competition.
I'm a little surprised, but that's the level I think I'll have if I can recover. It was fun that it worked so well.
“A little more fighting”
Hopes for the evening:
I hope I can race like this; it will probably be a little more challenging tonight, she says.
Is it important to win?
The result doesn't really matter that much, I just want to feel like I'm starting somewhere.
Three more Swedes are in the final: Louise Hansson had the third-best time (25.30), Sara Junevik the fifth (25.54) and Sofia Åstedt the sixth (25.60).
