With time bonuses, Dumoulin put 24 seconds into pre-race favourite Nairo Quintana (Movistar) on the summit finish. Quintana had a gap early on the climb, but the Dutchman from Maastricht returned and dropped him for the stage win and bonus seconds.
"It's very much still open," Dumoulin said, after riding though the press room on his black bike, pink tape wrapped around the handlebars to match his pink long-sleeve jersey.
"We have the last week, and we haven't even had half of the climbs yet. It will be very, very hard, and so much can happen. I am still a little bit afraid of the last week, so we will see."
The 26-year-old Sunweb rider has been in this position before in a Grand Tour, being to win the 2015 Vuelta a España before cracking on the penultimate stage. This year, however, he prepared for the first time to win a Grand Tour.
Watch: Giro d'Italia stage 14 highlights
Quintana struck with four kilometres left no the climb to Oropa and gained time with Domenico Pozzovivo (Ag2r La Mondiale) and Ilnur Zakarin (Katusha-Alpecin). Dumoulin, though, kept his rival insight, and passed him in the final two kilometres. Zakarin went to the front, while Quintana faded.
Dumoulin took over and charged for the line with the roar of fans covering the hillsides. Victory brought a 10-second bonus to add to the 14-second gap on Quintana.
"Now I have even more of an advantage," Dumoulin said. "It's a really nice advantage. We cannot sit back and relax, we have to stay focused. And then we will see what happens in the last week."
The Giro continues tomorrow with an Il Lombardia-esque stage to Bergamo. After a rest day the riders will climb the Stelvio twice, before four more stages in the mountains.. Dumoulin's pink light at the end of the tunnel is a 29.3-kilometre time trial from Monza to Milan on the last day.
"It's the number of high altitude climbs that worries me," Dumoulin continued. "I'm not afraid of my competition, I 'm not afraid of anything really, I just need to stay focused and it will be OK."
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Gregor Brown is an experienced cycling journalist, based in Florence, Italy. He has covered races all over the world for over a decade - following the Giro, Tour de France, and every major race since 2006. His love of cycling began with freestyle and BMX, before the 1998 Tour de France led him to a deep appreciation of the road racing season.
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