On a narrow but totally flat course, Cerny, who is about to celebrate his 30th birthday, was 29/100th ahead of the reigning time trial world champion, Norway's Tobias Foss (Jumbo-Visma), who paid for a badly negotiated final corner and is still waiting for a first individual success in his rainbow jersey.
Frenchman Rémi Cavagna (Soudal Quick-Step), an exercise specialist who won the 5th stage of the Tour de Romandie in 2021, finished 97/100th behind his teammate.
"I didn't expect to win, but to be in the Top 5 or Top 10," Cerny told RTS, describing a prologue as "fast, really painful and really tight" along the left bank of the Rhône, in chilly but stable weather.
The first wearer of the leader's jersey, returned to yellow for this 76th edition after a year in green, had so far only one prestigious victory, with the 19th stage of the Giro in 2020.
On the French side, Romain Bardet set the 26th fastest time at 16 seconds, his legs still heavy after Liège-Bastogne-Liège on Sunday, and is "especially looking forward to Friday and Saturday", with a hilly time trial and the queen mountain stage to Thyon 2000.
For the last season of his career, Thibaut Pinot - double stage winner on the Tour de Romandie in 2015 and 2016 and 2nd overall in 2016 - finished 80th in the prologue at 27 sec.
The Tour de Romandie continues on Wednesday with a bumpy stage between Crisser and Le Sentier, in the Vallée de Toux (Le Sentier).
© 2023 AFP