Chris Froome feared he had underperformed in Tuesday's time trial before crossing the line as the fastest rider on stage 16 of the Vuelta a Espana.
The Team Sky rider almost doubled his lead over Vincenzo Nibali in the general classification as only one rider came within 57 seconds of his time of 47 minutes.
But Froome - now just under two minutes ahead of the Italian - conceded he was not confident during the 40.2-kilometre route, fearing he would fall short.
"I was riding it at the speed I felt best," he said. "I wasn't really getting many time checks from the car, so I didn't really know where I was.
"I actually thought it wasn't good news, so I was worried halfway through. But coming into the last six or seven kilometres, I found out I was on track to fight for the stage. It was a big relief.
"I'm super, super happy to be in this position. It's an amazing feeling to extend my lead now and be in this position, with four days of big racing left now.
-- Team Sky (@TeamSky) September 5, 2017
"I'm going to take it one day at a time but I want to say a massive thanks to the support team at Team Sky. It's a huge part of being able to do what I'm able to do, having everything there to focus on the job at hand.
"I have a good buffer but the race isn't over, so I'll have to keep fighting every day and get one day closer to Madrid.
"Tomorrow [stage 17] is going to be absolutely brutal. Los Machucos, from what I can see, is a wall. It's a big GC battle for sure."