Two weeks after cruising to the opening-stage win, Olympic gold medalist Martinez was back in the winner's paddock after securing victory in near-perfect sailing conditions in the shadow of Table Mountain.
Once again, Camper led by Australian skipper Chris Nicholson, were forced to follow home in Martinez's wake with US-led Puma third.
The turning point came midway through the race when Cape, who put in a near-faultless leg-one performance picking a route through hazardous conditions from Alicante to Cape Town, correctly gauged changing wind directions with the ideal sail combinations.
Telefonica now lead the overall standings on 37 points, three clear of Camper (Spain/New Zealand), with France's Groupama 10 further adrift on 24 following a disappointing fifth spot on Saturday.
The second leg of the ocean race, from Cape Town to Abu Dhabi, begins on Sunday. In all, the race covers 39,000 nautical miles (72,000 kms) and visits 10 countries. It is due to finish in July in Galway, Ireland.
Three boats failed to finish the first leg but were back on the start line on Saturday.
A storm overnight in the Mediterranean on day one left Abu Dhabi without a mast and Sanya with a broken hull after hitting debris. Two weeks later, Puma, led by US skipper Ken Read, also lost her mast following a rigging failure.
She was shipped to Cape Town at the beginning of the week to have a new mast put in place, having spent several days awaiting rescue from Tristan da Cunha.
"I told a fib beforehand," Read told reporters. "I said we would settle just to get round this course in one piece but as you could see that wasn't the truth. We were going out there to win but we'll take that podium place. It was a good return."
