Wellens tore out of a severely reduced pack at the foot of the final short but steep climb to take a lone victory by five seconds on Mikel Landa (Movistar), with former leader Wout Poels (Team Sky) crossing the line at 13 seconds. Previously third overall, Wellens is now seven seconds ahead of Landa, with Poels dropping two spots to lie 11 seconds down.
The reshuffling of the top positions overall still leaves six riders within 32 seconds of Wellens, whilst Steven Kruiswijk (LottoNL-Jumbo) is a minute back, meaning the race is far from decided with a time trial still to come.
As a former winner of the Guangxi Tour, the Eneco Tour and the Tour of Pologne, Wellens has a strong palmares in week-long stage races and as he pointed out "I'm not leading this by accident."
"I knew on the second day I had really good legs from the second day. I also knew that the climb today was good for me, I took the chance I had," he said.
"Yesterday I did a lot of research on this climb, and that paid off. I had really good legs, I knew the final climb. The fact there were cobbles and you can ride next to the cobbles on the tarmac was really good for me."
Wellens was also willing to pay some mind games, saying that he had let Landa get something of a gap, and that he had initially feigned being weaker than he really was, so that way the Spaniard would keep riding hard.
"I was afraid to let him get too much of a gap, then in the last 250 metres I really went for it, and I was a little bit stronger than him today."
Wellens had initially doubted about his chances of success against Poels and the other time trialists for Sunday's showdown, but his morale appeared to have been boosted by this latest success. He will now start the 14km time trial last and wearing the leader's red jersey.
"When I said that, I didn't have the leader's jersey, but now I am really motivated. It's a special TT, I'm not really a specialist but the fact that it's on gravel roads" - for around six of the 14 kilometres - "could mean I have a chance. Of course I could have a chance of winning the GC. It's not every day that you ride on gravel roads, so we will know tomorrow."
Wellens also reiterated his opinion expressed earlier in the week that he did not feel it was a good idea for Chris Froome (Team Sky) to be at the Ruta del Sol. He insisted that he believed he was not alone in thinking that in the peloton.