Geraint Thomas lost the lead of the Tirreno-Adriatico after suffering a mechanical problem near to the finish of stage four.
The Team Sky rider was the joint leader with Greg van Avermaet overnight but came in 40 seconds behind Mikel Landa.
Welshman Thomas had to change his bike and was helped by team-mate Chris Froome to reduce the damage in the final kilometre of the summit finish.
But he dropped to fifth, 26 seconds behind new race leader Damiano Caruso.
The Italian leads from Team Sky rider Michal Kwiatkowski, by just one second with three stages remaining, the last of which is a 10km time trial.
Elsewhere, Britain’s Simon Yates moved into the overall lead at Paris-Nice with a solo victory on stage seven.
Stage four result:
1. Mikel Landa (Spa/Movistar) 6hrs 22mins 13secs
2. Rafal Majka (Pol/Bora-Hansgrohe Same time
3. George Bennett (NZ/LottoNL-Jumbo)
4. Fabio Aru (Ita/UAE Team Emirates) +6secs
5. Ben Hermans (Bel/Israel Cycling Academy) Same time
1. Damiano Caruso (Ita/BMC) 17hrs 14mins 49secs
2. Michal Kwiatkowski (Pol/Team Sky) +1sec
3. Wilco Kelderman (Ned/Team Sunweb) +11secs
4. Mikel Landa (Spa/Movistar) +20secs
5. Geraint Thomas (GB/Team Sky) +26secs
6. Rigoberto Uran (Col/EF Education First-Drapac) +31secs
7. George Bennett (NZ/Lotto NL Jumbo) +33secs
8. Davide Formolo (Ita/Bora-Hansgrohe) +34secs
9. Tiesj Benoot (Bel/Lotto-Soudal) 36secs
10. Domenico Pozzovivo (Ita/Bahrain-Merida) 41secs