Simon Yates described twin brother Adam as his “secret weapon” after a battling display in the Basque Country saw the British rider’s Vuelta a España lead trimmed in in Wednesday’s 17th stage.

Canada’s Michael Woods won in the mist on Balcon de Bizkaia, seeing off the challenge of Dylan Teuns, but it was the overall classification battle that caught the attention as Yates lost contact with his chief rival, Alejandro Valverde, on the final ramps of the brutal concluding climb, eventually ceding eight seconds to the Spaniard. That meant the 26-year-old – who saw his lead in the Giro d’Italia earlier this year overturned during a dramatic 19th stage on which Chris Froome took control of the race – leads by 25 seconds going into the final four stages and he admitted it could have been even closer had it not been for the efforts of his brother and the rest of his Mitchelton-Scott teammates.

“We employed our secret weapon in Adam over the last kilometres, that’s why we’ve been saving him for this final section of the race and Jack [Haig] was around the mark also,” said Yates. “The whole team were there today, and they did a fantastic job. I lost a few seconds in the sprint there in the end, it’s no shame to lose a few seconds to Valverde in a sprint and I put time into a few other people so all in all it was a good day.

“We expect aggressive, attacking racing from Valverde and Movistar – I don’t think he knows any other way to ride and he has a very strong team around him. Of all the stages left I was most afraid of this one but there’s still a lot of hard racing to come. Tomorrow should be a sprint day and we can hopefully take it a bit easier, although you never know, and then we have Andorra. I think those stages will suit me better than today but we’ll see.”

Michael Woods celebrates after winning the 17th stage. Photograph: Alvaro Barrientos/AP

A flat stage is scheduled for Thursday, so the best hope of Yates’s rivals to wrest the red jersey from his shoulders will come at the concluding climb of Friday’s stage and then in Saturday’s mountainous 20th stage, the 97.3km route from Andorra Escaldes-Engordany to Coll de la Gallina.

Of the red jersey contenders, only Spain’s Enric Mas was able to stay with Valverde. Mas was 14th and Valverde 15th on the stage, with Yates 17th. The Dutchman Steven Kruijswijk and Colombia’s Nairo Quintana, the 2016 winner, lost more than a minute to Valverde as they finished together in 22nd and 23rd place, respectively.

Mas moved up from fifth to third as a result, one minute 22 seconds behind Yates. Miguel Ángel López is now fourth, with Kruijswijk fifth, and Quintana more than two minutes behind in sixth.

“I had spoken with Nairo and he had told me he was feeling good,” said Valverde. “Then, with such humidity and the changes of temperature, anything can happen. Maybe he felt a bit the efforts from the time trial. We’ll speak in the hotel to see what we can do from now on. Enric is third, of course he can win La Vuelta. It’s difficult but he’s going step by step. I’m not so far either.”