The Spanish rider was one of a number of men to bridge across to the breakaway midway through the fast 189km stage from Molfetta to Peschici, and made sure he was constantly towards the front of affairs on a thrilling and ever-changing day of racing in eastern Italy.
With 36km to go he was one of four riders to follow an attack by Valerio Conti (UAE Team Emirates) as the Italian, two minutes down in the general classification, tried to move into the pink jersey.
However as they approached the uphill finish into Peschici it was clear that the break wouldn't have enough of an advantage for Conti to take pink, especially as a surprising, and ultimately unsuccessful, attack from Team Sky's Mikel Landa raised the pace behind.
The stage win was still up for grabs, and Conti looked to be the strongest as he attacked with 800m to go, but suffered heart break as his bike slipped from underneath him on a hairpin bend.
That opened the door for Izagirre, who was best-placed to come around the stricken Italian, opening a gap over Luis Leon Sanchez (Astana) and Giovanni Visconti (Bahrain-Merida) that he was able to hold to the line.
Only a few seconds behind, the general classification contenders all finished together, meaning Bob Jungels stays in pink for tomorrow's summit finish up the Blockhaus.
How it happened
The opening of the eighth stage of the Giro d'Italia saw some of the most aggressive riding that the race has seen so far, with a huge fight to get in the break and 56km covered in the first hour.
When a move finally went clear after nearly 60km it consisted of 16 riders: Laurent Didier (Trek-Segafredo), Kristian Sbaragli (Dimension Data), Maciej Paterski and Branislau Samoilau (CCC Sprandi Polkowice), Jasper De Buyst (Lotto Soudal), Viacheslav Kuznetsov (Katusha-Alpecin), Roberto Ferrari (UAE Team Emirates), Mirco Maestri and Vincenzo Albanese (Bardiani-CSF), Iljo Keisse (Quick-Step Floors), Chris Juul-Jensen (Orica-Scott), Alex Howes (Cannondale-Drapac), Luis Leon Sanchez (Astana), Jan Barta, Lukas Pöstlberger and Gregor Mühlberger (Bora-Hansgrohe).
That break satisfied most, but not Wilier Triestina and Gazprom-Rusvelo, neither of whom were represented, who then set a fierce pace on the front of the bunch to limit the break's advantage to just 1-30 by the base of the second category climb of Monte Sant'Angelo with 100km remaining.
The chances of a breakaway win seemingly diminishing with the shrinking gap, Sanchez decided it was time to go solo, jumping clear of the break on the climb.
The fierce pursuit saw a number of riders dropped from the break on the 10km climb, while a few riders also took the opportunity to jump across from the peloton.
By the top of the climb Sanchez held an advantage of around a minute over a chase consisting of eight riders: Pöstlberger, Samoilau, Mühlberger, Didier and Sbaragli from the original break, and Visconti, Conti and Davide Villela (Cannondale-Drapac) who had come across from the peloton, which itself was just under two minutes back.
The chasing group was bolstered with the addition of four more riders in Ivan Rovny (Gazprom-Rusvelo), Gorka Izagirre (Movistar), Julen Amezqueta (Wilier Triestina) and Clement Chevrier (Ag2r La Mondiale), with the extra fire power being enough to catch Sanchez with 70km remaining
One team which wasn't represented up the road was Bardiani CSF, who attempted to rectify that by sending two riders - Nicola Boem and Enrico Barbin - off the front of the peloton.
The two men in green made short work of the gap, riding across in only a handful of kilometres to create a 14 rider move at the front of the race.
For the first time on the stage, everyone seemed happy for the race situation, enabling the break to extend its advantage out beyond four minutes which was enough to put Conti, just over two minutes down at the start of the day, into the virtual maglia rosa.
However, Quick-Step Floors, working for race leader Bob Jungels soon decided that the break had gone out too far, and moved to the front of the peloton to bring the gap back down to two minutes.
With his eyes on pink, Conti decided to take matters into his own hands with 36km to go, attacking out of the front group, dragging Sanchez, Visconti, Mühlberger, and Izagirre with him.
That move increased the gap beyond three minutes once again, and enabled Conti to take three bonus seconds at an intermediate sprint with 30km remaining, but Quick-Step were determined to protect Jungels' lead and once again brought the gap back to two minutes with 15km to go.
Desperate to move into pink, Conti attacked from the break with 11km to go, but was unable either extend his advantage over the peloton or to shed his breakaway companions as Izagirre quickly moved onto his wheel.
However that provided an invitation for a counter-attack, and Giovanni Visconti duly obliged, quickly opening a small gap that Conti fought desperately to close down, pulling Sanchez and Izagirre across in the process but dropping Mühlberger.
In the peloton most of the GC contenders would have been expecting to rest their legs ahead of tomorrow's summit finish up the Blockhaus, but Mikel Landa had other ideas, launching a surprise attack with 10km remaining.
The Spaniard's move caught everyone off-guard, forcing Team Sunweb, Movistar, FDJ, and LottoNL-Jumbo to chase as he opened a gap of 15 seconds, before being brought back after a nervous few minutes for many
Meanwhile Izagirre attacked from the break, with only Visconti initially able to follow, with Sanchez and Conti taking a couple of minutes to finally make their way across.
With three kilometres to go their advantage was down to a minute, meaning no pink jersey for Conti, but a stage win certainly up for grabs.
Under the flamme route and Conti attacked, but he went into a hairpin too fast, lost his front wheel and hit the deck.
That opened to door for Izagirre, who stayed on the power and simply rode away from Sanchez and Visconti to take his first Grand Tour win in his ninth attempt at one of cycling's three biggest stage races.
By this point the peloton was only a few seconds behind the break, with Enrico Battaglin (LottoNL-Jumbo) leading the GC contenders across the line.
Race leader Bob Jungels finished safely in tenth place to maintain his six second lead over Geraint Thomas (Team Sky) in the pink jersey standings going into tomorrow's crucial summit finish up the Blockhaus.
Giro d'Italia 2017, stage eight: Molfetta to Peschici (189km)
1. Gorka Izagirre (Esp) Movistar, in 4-24-59
2. Giovanni Visconti (Ita) Bahrain-Merida, at 5 secs
3. Luis León Sanchez (Esp) Astana, at 10 secs
4. Enrico Battaglin (Ita) Team LottoNl-Jumbo, at 12 secs
5. Michael Woods (Can) Cannondale-Drapac
6. Thibaut Pinot (Fra) FDJ
7. Vincenzo Nibali (Ita) Bahrain-Merida
8. Adam Yates (GBr) Orica-Scott
9. Steven Kruijswijk (Ned) Team LottoNl-Jumbo
10. Bob Jungels (Lux) Quick-Step Floors, all at same time
General classification after stage eight
1. Bob Jungels (Lux) Quick-Step Floors, in 38-21-18
2. Geraint Thomas (GBr) Team Sky, at 6 secs
3. Adam Yates (GBr) Orica-Scott, at 10 secs
4. Vincenzo Nibali (Ita) Bahrain-Merida
5. Domenico Pozzovivo (Ita) Ag2r La Mondiale
6.Tom Dumoulin (Ned) Team Sunweb
7. Nairo Quintana (Col) Movistar
8. Bauke Mollema (Ned) Trek-Segafredo
9. Andrey Amador (CRc) Movistar
10. Thibaut Pinot (Fra) FDJ, all at same time
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