Renshaw, more used to working as Mark Cavendish’s lead-out man within the Omega Pharma-Quick Step squad, jumped clear before the line to win comfortably as Team Sky’s Swift paid the price for going too soon.
After the climb of the Great Orme created significant splits in the peloton, Movistar’s Alex Dowsett tried to break away to victory – challenged by Sylvain Chavanel (IAM Cycling) – but Sir Bradley Wiggins, working for Swift, led a group of chasers back on to their wheel on the approach to the line.
Swift then sprang forward but, with Cavendish not in contention, Renshaw covered the move and claimed the win. The 31-year-old takes the yellow jersey from Marcel Kittel, who lost touch with the peloton on the Great Orme.
Alberto Contador won a battle of the heavyweights against Chris Froome but before they sparred at the finish, two other riders were disqualified on stage 16 of the Vuelta a Espana for exchanging punches on the road.
Contador claimed his first stage win at La Farrapona to extend his overall lead.
Contador’s Tinkoff-Saxo team-mate Ivan Rovny and Omega Pharma-Quick Step’s Gianluca Brambilla had come to blows while part of the day’s breakaway.