Stage 17, a long 202 km transitional day from Cassano d'Adda to an uphill finish at Andalo, was destined for the break from the gun. Attacks flew from the start before Niklas Larsen, Jan Christen, Rémi Cavagna, Michael Valgren, Alessandro Tonelli, Manuele Tarozzi and Andreas Leknessund finally got clear, stretching their lead to two minutes. A chasing group formed almost immediately, and before the summit of the Passo dei Tre Termini, Davide Bais, Lorenzo Milesi, Mick van Dijke and Frank van den Broek bridged across to the leaders. A larger third group containing Jhonathan Narváez, Enric Mas, Einer Rubio, Giulio Ciccone, David de la Cruz, Aleksandr Vlasov and others crested the climb around 50 seconds back, with the peloton drifting steadily out of contention.
On the Cocca di Lodrino, Rémi Cavagna pushed on alone while the groups behind merged. The Frenchman built a two-minute gap on the chasers and six minutes on a peloton content to let the day go, but on the climb to Roncone he was reeled in. At the Roncone summit Narváez took the intermediate sprint to reclaim the maglia ciclamino from Paul Magnier.
Valgren, Caruso, Leknessund, Juan Pedro López and Gianmarco Garofoli forced the front split, then Rubio, Vlasov, Igor Arrieta, Van Dijke and De la Cruz joined to make a ten-man leading group with roughly 30 km to go. On the Andalo Lever climb Rubio attacked and briefly distanced everyone before Valgren and Arrieta clawed back; the leaders crested with a slim lead over the chase. The six leaders regrouped inside the final two kilometres, and Valgren kicked clear just before the flamme rouge. He opened an instant gap; Leknessund launched the chase but it was too late. Valgren soloed home for an emotional maiden Grand Tour stage win, with the GC group arriving more than five minutes down and the overall picture unchanged.