Denifl attacked out of a breakaway with five kilometres to go to hold off a brave chase by Alberto Contador to win a brutal, mountainous 180.5km stage from Villadiego Los Machucos in 4hr 48min 52min.
Contador was 28sec back to aid his chances of making the general classification podium with Colombia’s Miguel Angel Lopez 1min 04sec down in third.
Froome has looked assured in his bid to become just the third rider to win the Tour de France and Vuelta in the same year.
But he seemed to pay for his efforts in winning Tuesday’s time trial as he cracked on the final climb and couldn’t stay with Nibali. The Italian finished alongside Lopez in fourth with Froome down in 14th. “I paid a little bit for yesterday’s effort for sure, but I am still in a fantastic position,” said Froome.
“Still over a minute to second place, so it’s a good buffer and I’m confident about the next few days ahead.”
The Briton has three more competitive stages to defend his lead before Sunday’s traditional parade around Madrid with the queen stage up the Alto de l’Angliru still to come on Saturday.
“If you include yesterday, this is a five-day block now,” added Froome. “I’m taking it one day at a time, knowing that stage 20 is going to be the hardest day of this block.
“Certainly any effort yesterday, today, it’s all going to compound up into stage 20 in the grand finale up Angliru.
“Otherwise, I’m feeling good, optimisitic about what lies ahead.
‘Enjoy it to the max’
Denifl’s win is by a distance the biggest in Irish team Aqua Blue Cycling’s short history.
Aqua Blue needed an invite to take part in the race in their first year as a professional team and also had to overcome the misfortune of their team bus being hit by an arson attack earlier in the event. “It’s been an amazing year for our team,” said Denifl.
“In the first year in pro Cycling we are here at the Vuelta and winning a stage, it is perfect.”
Denifl was part of an early six-man breakaway and stayed out in front of the general classification favourites despite immense pressure from Contador in the final stages. The Spanish veteran didn’t get the stage win he desired in his final race before retirement. However, Contador, a three-time Vuelta winner, is now just 1min 21sec down on Wilco Kelderman in the battle for the podium as he remains fifth overall. “It was a shame not to get the stage win for the team and the fans, but there are still three hard days to come,” said Contador. “I have four days left as a professional cyclist and I’m going to enjoy it to the max.”
The terrain eases slightly for the 169km 18th stage from Suances to Santo Toribio de Liebana today.
Classification after Stage 17
1. Chris Froome (Britain/Team Sky) 67:44:03”
2. Vincenzo Nibali (Italy / Bahrain-Merida) +1:16”
3. Wilco Kelderman (Netherlands / Team Sunweb) +2:13”
4. Ilnur Zakarin (Russia / Katusha-Alpecin) +2:25”
5. Alberto Contador (Spain / Trek-Segafredo) +3:34”
6. Miguel Angel Lopez (Colombia / Astana Pro Team) +4:39” 7. Michael Woods (Canada / Cannondale-Drapac) +6:33”
8. Wout Poels (Netherlands / Team Sky) +6:40”
9. Fabio Aru (Italy / Astana Pro Team) +6:45”
10. David De La Cruz (Spain / Quick-Step Floors) +10:10”
11. Steven Kruijswijk (Netherlands / LottoNL-Jumbo) +10:13” 12. Esteban Chaves (Colombia / Orica-Scott) +10:46”
Gaviria takes Tour of Britain’s 4th stage
Fernando Gaviria held his nerve to win the Tour of Britain’s fourth stage after a tense duel with Team Sky’s Elia Viviani yesterday.
Quick-Step Floors rider Gaviria held off Viviani and Alexander Kristoff to take the 165-kilometre stage from Mansfield to Newark.
While Colombia’s Gaviria won the daily honours, Viviani assumed the overall lead from Caleb Ewan.
Ewan is level on time with Viviani with four stages remaining, but the Orica-Scott star has lost the green jersey with the Italian boasting greater consistency.
Gaviria now sits third but trails by just six seconds, with Thursday’s fifth stage a 16km time trial in Essex’s Clacton-on-Sea.
“I’ve been coming back from an injury on my left leg. Every day has been going a little bit better. Today everything felt good,” Gaviria said.
Meanwhile, Brent Bookwalter of the United States was forced out of the race after an ugly pile-up. Bookwalter crashed into a car parked close to a tight corner and was forced to withdraw from the race, in an incident where several other riders also crashed.