The route for this Tour of California is one of the toughest in the race's history but it began with a pan-flat stage that featured three laps of a finishing circuit in downtown Sacramento, making it akin to a criterium race.
In an aggressive finale, in which Geroge Bennett (Jumnbo-Visma) nabbed a bonus second at an intermediate sprint, the bunch started to split under the force of the lead-out. Team Ineos took control for Kristoffer Halvorsen but Sagan was on his wheel and surged clear on the right-hand side of the road. He was pushed all the way to the line by the USA's Travis McCabe, with Max Walscheid (Sunweb) taking the final podium position ahead of a fading Havlorsen.
For Sagan it was his 17th stage win at California, and he takes the first leaders' jersey of the race.
Watch how it all unfolded in the highlights video above.