Dumoulin produced a composed performance on the steep slopes of the Ermita de Alba, giving away less than 30 seconds to general classification rivals Joaquim Rodriguez (Katusha), Fabio Aru (Astana) and Rafal Majka (Tinkoff-Saxo).
Currently sitting fourth on GC with a deficit of 1 min 51 secs to red jersey wearer Rodriguez, Dumoulin is expected to overhaul all those ahead of him during the 38.7km time trial on Stage 17 after tomorrow's rest day.
Dumoulin sounded quietly confident after Stage 16.
"That was much better than expected. I didn't feel so good on the first-category climb, but I was never really in trouble." he said after the stage.
"I thought, 'ah we'll give it a go on the last climb'. I had really good legs, to lose 28 seconds is really really good. Today I thought 'OK, I’m just going to go and when I blow up I blow up', but I didn't."
His attention now turns to Wednesday's race against the clock. The time trial's profile could not be better for him, with barely any climbing of note. Giant-Alpecin directeur sporitif Addy Engels is confident that Dumoulin will take the race lead.
“Tom could take four seconds per kilometre,” Engels told VeloNews.
That kind of margin would see Dumoulin gain around two and a half minutes on his rivals, putting him around 40 seconds in the lead. While that's a sizeable margin, it's not unassailable - and it means this race is likely to go all the way to Madrid - a fact Dumoulin is clearly aware of.
"That [overall win] will be very difficult. There will become hard stages coming up in the next week, but it's looking good now.
"Everything depends on the time trial, but even if my time trial is really good, there will be three hard days to go.”