Stage 4 was the 23.7 km individual time trial in Aarburg — the day circled on the route as the GC-defining test. World-class against the clock, Marlen Reusser delivered exactly the ride Movistar needed, stopping the clock at 29:36.46 for an average of 48.028 km/h, the fastest time of the day by a clear margin.

Zoe Bäckstedt, a strong time triallist herself, was the best of the rest at 11 seconds. Loes Adegeest (+0:54) and Franziska Koch (+1:02) rounded out the top four. Crucially, race leader Elisa Longo Borghini limited her loss to 1:04 for fifth on the stage — a respectable ride against a specialist, but not enough to keep the jersey. Reusser's win moved her into the overall lead by 10 seconds over Longo Borghini, with the final mountain stage at Villars-sur-Ollon left to settle the race.

Marlen Reusser leads the general classification after stage 4 with a total time of 8:51:25. Elisa Longo Borghini is second at just 10 seconds, Cédrine Kerbaol third at 1:20, Sarah Van Dam fourth at 1:35 and Femke de Vries fifth at 1:43. Niewiadoma sits sixth at 1:49 and Le Court-Pienaar seventh at 2:01. The slender 10-second margin sets up a decisive showdown on the stage 5 mountain stage to Villars-sur-Ollon, where the pure climbers — Longo Borghini chief among them — will look to overturn the time trial deficit. In the jersey competitions, Bäckstedt leads the points classification, De Vries the mountains (QOM) classification, and Kerbaol the young rider classification.