It means Cavendish lies 34 seconds behind overall leader Lars Boom of Rabobank, ahead of Sunday’s climax to the race in central London.
But with stages today and tomorrow, before two separate parts to the finale in the capital, there is more than ample time for the Manxman to catch up.
An initial breakaway soon faltered on a testing, hill-packed, 111 mile-stage from Exeter to Exmouth.
Frenchman Damien Gaudin of Team Europcar the tried to pull clear as the course approached its conclusion.
However he too was reeled in, and with less than two miles left the leading pack manoeuvred Cavendish and Renshaw to the front.
The colleagues went head-to-head in the final push for the line, with Australian Renshaw just pipping the Tour de France green jersey winner.
Sunday’s stage in London incorporates an individual time trial and a circuit race, which starts and finishes on Whitehall.