Having chased down every move by Fabio Aru (Astana) on the last climb of La Quesera despite being isolated from his own team, and Astana's considerable collective mountain strength, Dumoulin even put in a dig of his own some four kilometres from the line.
Dumoulin, in his fifth day in the red jersey, even joked to Spanish TV after the stage: "There's three stages left, three days, so I can lose one second a day."
"It was a hard day," Dumoulin said, "but I'm still in red, I could handle those attacks. I knew he [Aru] had spent some energy, so when [Dani] Moreno [Katusha] tried a move late on, I made a counter-attack of my own."
Dumoulin said that his confidence had grown during the stage because despite Aru's surging attacks on the undulating ascent of the Quesera, "after the first one, I knew it'd probably be another day in red."
"Of course it hurt, that first attack was very strong, but I always kept his wheel, even when it got steeper."
"It was a big boost to my confidence, and 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."
On paper, Friday's stage from Medina del Campo to Avila is the easiest of the three stages between Burgos time trial and Madrid, with just one third category climb and one second. But whilst Dumoulin has had one good day in the mountains, he knows that Aru will be keen to snatch the slightest opportunity to return to red.