Team Sky's Geraint Thomas moved into the lead at Tirreno-Adriatico, where Chris Froome finished with the leaders to leap into the top three.
Thomas finished fourth on a gruelling third stage into Trevi, finishing the 234km course seven seconds adrift of winner Primoz Roglic (Lotto-NL Jumbo).
But the Welshman managed to claim three seconds on the rest of the peloton, and his finish was enough to secure the blue jersey, ahead of BMC Racing's Greg van Avermaet on countback.
Froome is three seconds behind that pair in third place and another Team Sky rider - Michal Kwiatkowski - rounds out the top five, just nine seconds behind Thomas.
Roglic, a stage winner at the 2017 Tour de France, was stepping on to the top of the podium for the first time this season.
He launched an attack with just over a kilometre remaining and, although Adam Yates (Mitchelton-Scott) gave chase, the Briton's late effort was in vain as the Slovenian time-trial ace held on.
The complexion of the race is likely to change again on Saturday when the peloton takes on a 219km stage from Foligno to a summit finish in Sarnano Sassotetto.