(CNN) -- Chris Froome retained the yellow jersey on a day of toil and trouble as Ireland's Dan Martin won the ninth stage of the Tour de France. 

Sky Team rider Froome, who has a one minute and 25 second lead over his closest challenger, was forced to battle on his own as his teammates failed to give him adequate protection. 

Richie Porte lost his grip on second place overall after finishing more than 17 minutes adrift, while Vasili Kiryienka was swept up by a broom wagon and is unlikely to feature in the remainder of the Tour. 

There was also misery for Peter Kennaugh, who suffered bruising after falling from his bike -- an incident which left Froome wide open to attack on all fronts. 

"This was one of the hardest days I have ever had on the bike," Froome told reporters. 

"I had no-one else with me. I am really happy I have come through today. I was completely on my own, I had (sporting director) Nicolas Portal in the car telling me not to worry." 

Martin, the nephew of great Irish cyclist Stephen Roche, won the long descent to Bagneres-de-Bigorre with Froome following home 20 seconds later in a pack which included rivals Alejandro Valverde and Alberto Contador. 

Team Sky principal Dave Brailsford revealed his surprise at seeing his team struggle with Porte's failure particularly difficult for him to comprehend. 

"That was a bit of a surprise, it is not often we've seen Richie have a day like that," Brailsford said. 
Who finished over 17 minutes back?
Richie Porte