The Giant-Alpecin rider looked confident and composed as he marked his general classification rivals, particularly Fabio Aru (Astana), throughout the 204km stage from Roa to Riaza.
Dumoulin even had the stones to put in a small attack of his own at 4km to go, firing a warning shot across the bows of those who hoped the Dutchman was hoping to hold on to his slim lead by the skin of his teeth.
"It was a hard day," Dumoulin said, "but I'm still in red and I could handle those attacks. I knew [Aru] had spent some energy, so when Dani Moreno (Katusha) tried a move late on, I made a counter-attack of my own."
Dumoulin added that he knew he would retain the red jersey after surviving Aru's first attempt to distance him.
"Of course it hurt, that first attack was very strong, but I always kept his wheel, even when it got steeper," he said.
"I know that Astana's strategy is to isolate me and get me out of the red jersey. But I know if I stay on Aru's wheel, then they cannot do anything."
Dumoulin is clearly ready for the inevitable attacks that will beset him on the remaining two stages before the final procession into Madrid.
“There will be two difficult days to come, where a lot can happen," he said.