Ripping downwind with hulls flying from the Golden Gate Bridge to Alcatraz, the two Oracle Team USA catamarans dominated the America’s Cup World Series on Thursday, a day Oracle skipper Jimmy Spithill said pushed him “to the limit” against a full fleet of 10 other boats.

Thousands of spectators crowded the Marina Green shoreline to watch the second day of racing in 45-foot catamarans, the prototype boats for the 72-footers that will race in the America’s Cup finals on San Francisco Bay next summer. Racing continues through Sunday.

The Oracle skippers, Spithill and Russell Coutts, are considered two of the finest America’s Cup skippers alive. Coutts, 50, has won four America’s Cup championships and is the CEO of Larry Ellison’s Oracle Racing. Spithill, 33, was the youngest helmsmen ever to win the America’s Cup in 2010 aboard Ellison’s trimaran, USA 17. He is now the defending champion who will race against the winner of the Louis Vuitton Cup challenger series next summer.

But another factor also contributed to their success Thursday, with Coutts winning the first fleet race and Spithill winning the second. Spithill also won a quarterfinal match race against Luna Rossa Piranha earlier in the afternoon.

“They know these waters better than any other team, and it shows,” said Tucker Thompson, a sailor who announced the play-by-play of the races for the crowds lining four deep along the sea wall at Marina Green. With their base camp at Pier 80 south of the Bay Bridge, Oracle Racing crew members have been practicing on the bay for more than a year.

Indeed, on more than one windward leg heading toward the Golden Gate in the second fleet race, Spithill held the lead by avoiding the current in the middle of the bay and staying close to the sea wall beside Fort Mason and the rocky jetty in front of the St. Francis and Golden Gate yacht clubs.

Eight teams competed Thursday in 11 boats, with several teams — including Oracle, Italy’s Luna Rossa and Sweden’s Artemis Racing — racing two catamarans each.

Coutts won the first fleet race, starting strongly and maintaining the lead throughout the race, with Spithill right behind him the whole way.

“You still got some tricks, you ol’ bugger,” Spithill, from Australia, said in a post-race interview.

Coutts, for his part, said he appreciated the slightly lighter winds — blowing less than 20 mph Thursday.

“It’s good for the old guys, mate,” said Coutts, from New Zealand. “It was a lighter day, but still really good racing.”

After Coutts and Spithill took first and second in the first fleet race, Luna Rossa Piranha took third. Ben Ainslie, a four-time gold medalist from Britain and fresh from the London Olympics, was a disappointing 10th.

In the second fleet race, Spithill was trailed by Artemis Red and Artemis White. Ainslie fared better, coming in fifth ahead of Coutts in sixth.