Colombian climber Nairo Quintana pulled on the leader's blue jersey after a solo finish to win the fourth stage of the Tirreno-Adriatico on Saturday.
The Movistar rider broke away from his rivals with two kilometres to go, crossing comfortably ahead of the British duo of Sky's Geraint Thomas, at 17 seconds, and Orica's Adam Yates at 23 seconds.
"I wasn't sure of what I could do today as I had been sick a few days ago but our tactic was to have someone ahead before I launched my attack and that's what happened with (Jonathan) Castroviejo," said Quintana of his Spanish teammate.
The win after 187km between Montalto di Castro and Monte Terminillo allowed the South American to take the overall race lead from Australian Rohan Dennis.
"The advantage I have on GC (general classification) now is significant. It gives me some confidence ahead of the second half of the race."
Sunday's mountainous fifth stage covers 210km from Rieti, through the Apennine Mountains before seven steep climbs to the Torretta pass, towards the finish line at Fermo.