Nieve had been part of a large 20+ rider escape group that got away in the early part of the stage, but was able to pull away from everyone but Joe Dombrowski (Cannondale) on the slopes of the penultimate climb of the day, the category one Cima Porzus.
But Dombrowski wasn’t able to hold the Spaniard’s wheel for too long, as he was able to put a 30 second gap into the American who was joined by Giovanni Visconti (Movistar) behind.
Nieve hit the summit of that climb with 44 seconds in hand, with just the category two climb of Valle to come. Once he’d made it two thirds of the way up that climb, it became his to lose with just 15km of the descent and flat to the finish line in Cividale del Friuli.
Visconti eventually distanced Dombrowski and made chase down the descent, but wasn’t able to any inroads to the man out front, with Nieve comfortably rolling home to take the victory with 43 seconds to spare.
It’ll be a relief for Team Sky after they lost their team leader Mikel Landa to illness earlier this week, with an impressive stage win on one of this Giro’s toughest day’s.
The favourites group behind was heavily reduced when they hit the penultimate climb of the day, with race leader Bob Jungels and Andrey Amador struggling towards the top of Cima Porzus.
Amador then attacked on the descent, with Vincenzo Nibali (Astana) following, but it was everyone together as they came to the bottom of the final climb.
Italian champion Nibali was the first to try an attack, with the likes of Alejandro Valverde (Movistar), Steven Kruijswijk (LottoNL-Jumbo), Esteban Chaves (Orica-GreenEdge), Rigoberto Uran (Cannondale) and Rafal Majka (Tinkoff) all present and able to follow.
Costa Rican Amador, who sat 24 seconds off of the lead at the start of the day, was able to stick with the group as Jungels fell to around 25 seconds behind.
The favourites then stuck together to the summit and down the descent, with Jungels slipping further behind. Nibali was then able to beat Valverde for the six second time bonus on the line, with Amador rolling in towards the back of that group.
Gianluca Brambilla then put in a hard effort to drag his Etixx teammate to the line, with Luxemborug champion Jungels coming in 2-07 down on Nieve and 50 seconds behind the group of favourites.
That meant Amador jumped into the lead of the overall classification, with Jungels 26 seconds behind in second place. Vincenzo Nibali moves up to third in the GC, now just 41 seconds behind.
Giro d’Italia stage 13, Palmanova – Cividale del Friuli (170km):
1. Mikel Nieve (Esp) Team Sky, in 4-31-49
2. Giovanni Visconti (Ita) Movistar, at 43 secs
3. Vincenzo Nibali (Ita) Astana, at 1-17
4. Alejandro Valverde (Esp) Movistar
5. Rafal Majka (Pol) Tinkoff
6. Stefan Denifl (Aut) IAM Cycling
7. Steven Kruijswijk (Ned) LottoNL-Jumbo
8. Rigoberto Uran (Col) Cannondale
9. Matteo Montaguiti (Ita) Ag2r La Mondiale
10. Domenico Pozzovivo (Ita) Ag2r La Mondiale, all same time
17. Bob Jungels (Lux) Etixx-Quick Step, at 2-17
Overall classification after stage 13
1. Andrey Amador (CRC) Movistar, in 54-05-50
2. Bob Jungels (Lux) Etixx-Quick Step, at 26s
5. Vincenzo Nibali (Ita) Astana, at 41s
3. Alejandro Valverde (Esp) Movistar, at 43s
4. Steven Kruijswijk (Ned) LottoNL-Jumbo, st
6. Rafal Majka (Pol) Tinkoff, at 1-37
7. Ilnur Zakarin (Rus) Katusha, at 2-01
8. Esteban Chaves (Col) Orica-GreenEdge, at 2-19
9. Rigoberto Uran (Col) Cannondale, at 2-48
10. Jakob Fuglsang (Den) Astana, at 3-15