Grousset had signed the 8th time in perfect equality with the Brazilian Bruno Fratus (21 sec and 83/100).
But it is the Frenchman who, thanks to a new time of 21sec59 in the play-off, will take part in the final scheduled for Friday.
Florent Manaudou, silver medalist in the 50m freestyle at the Tokyo Games last summer, only got the 11th time in the semi-finals with a time of 21sec 95/100.
"It's my level of the day. It helps to put ideas back in place" reacted to the microphone of France 4 the quadruple world champion in long pool (one title in 2013, three in 2015).
"It proves that talent is not enough and that you have to work. I worked less so it does not pass," he added.
© 2022 AFP