SAN FRANCISCO >> Nothing but stern.

That’s mostly what defending America’s Cup champion Oracle Team USA saw of Emirates Team New Zealand’s fast boat on Thursday, when the plucky Kiwis won two more races to move closer to taking the America’s Cup Down Under for the second time in 18 years.

Of course, since this newfangled America’s Cup is sailed in high-performance, 72-foot catamarans, Oracle and its new tactician, Olympic star Ben Ainslie, had to watch two Kiwi sterns speed past and then pull away between Alcatraz Island and the Golden Gate Bridge.

There’s only one upwind leg on the five-leg course on San Francisco Bay, and that’s where the Kiwis are burying the Americans as the boats zigzag toward the Golden Gate Bridge.

With their grinders working so hard they were gasping for air, and skipper Dean Barker making an aggressive move, the Kiwis turned a close Race 6 into a 47-second victory. They then put a whitewashing on Larry Ellison’s syndicate in the seventh race, leading the whole way for a victory of 1 minute, 6 seconds.

The Kiwis relocated from their small island country of 4.5 million people to San Francisco earlier this year with the singular intention of ripping the oldest trophy in international sports away from the American powerhouse. They lead 6 to minus-1 and need three more victories to claim the Auld Mug for the Royal New Zealand Yacht Squadron.

The way the Kiwis are sailing, the clincher could come Sunday afternoon on San Francisco Bay. Friday is a lay day, with Races 8 and 9 on Saturday. Two more races are scheduled for Sunday, the second one if necessary.

Barker was at the wheel when Team New Zealand, beset by major breakdowns, lost the America’s Cup in a five-race sweep by Alinghi of Switzerland in 2003. He got the Kiwis back to the finals in 2007, only to lose 5-2 to the Swiss.

“We wouldn’t be here if we weren’t driven,” Barker said. “Team New Zealand exists to win the America’s Cup. It’s why we’re here. We’ve got an opportunity, but we’ve still got to go out and perform well on the water.”

The deep, well-funded American syndicate — which now has only one American on its 11-man crew — is in deeper trouble than it was two days earlier, when a tactical blunder crushed what momentum it had gained from its only victory, in Race 4.

Oracle Team USA, owned by software billionaire Ellison of Oracle Corp., was docked two points in the biggest cheating scandal in the 162-year history of the America’s Cup. It still needs to win 10 races to keep the silver trophy at the Golden Gate Yacht Club.

Replacing tactician John Kostecki with British Olympic star Ben Ainslie simply can’t make up for the fact the Kiwis are faster and better sailing upwind toward the Golden Gate Bridge.

“We cannot give up and I can guarantee we won’t do that,” Oracle skipper Jimmy Spithill said. “We’ll keep fighting the whole way till the end. There’s still a lot of racing; I’m still convinced we can win races. Sure we made a change in the back of boat. Both John and Ben are fantastic sailors, two of the best sailors in the world, so we’re very fortunate we can rotate guys like that. But we have to study the data and really see what we can do to change up the boat.”

Ainslie won four straight Olympic gold medals as well as a silver for Britain. The 36-year-old was knighted in March.

Until Thursday, Ainslie had served as helmsman of the backup boat, helping to prep Spithill for the regatta. The move had been expected since Kostecki called for a foiling tack that the American syndicate botched in a punishing loss in Race 5 on Tuesday.

Barker got everything right in the seventh race and the Kiwis turned a 7-second lead at the leeward gate into a 56-second lead at the windward gate inside the Golden Gate Bridge.

Race 6 was a classic. It exhibited what’s becoming known as the “Kiwi stretch,” when Team New Zealand speeds ahead sailing upwind.

Spithill led by 12 seconds at the downwind second gate. Kiwi tactician Ray Davies called for an extra gybe sailing the downwind second leg, which allowed Team New Zealand to split from Oracle on the upwind third leg and gain starboard tack advantage.

The Kiwis began reeling in the American syndicate during a fierce tacking duel past Alcatraz Island that left the grinders struggling Among the Kiwis who turn the winches that power the hydraulic system for the daggerboards and trims the sails are Rob Waddell, an Olympic rowing gold medalist and former two-time world champion, and Grant Dalton, the 56-year-old syndicate head.

“We’re stoked with the way today went,” said Glenn Ashby, an Australian who expertly trims the wing sail on the Kiwi cat. “This was a bit of a pivotal day for us in the campaign. I think the boys certainly sailed a fantastic first race and second race, but particularly in the first race where we were sort of back to the wall. A third of the way through the race the guys dug really deep and I’ve never seen some of the performance out of the handles that those guys were wanting today.”

After two lead changes, the boats crossed for a third time. Barker pulled an aggressive move and pointed his cat at Oracle as they crossed, forcing it to do a deeper turn. The Kiwis began pulling away sailing in light wind and led by 44 seconds at gate three.

Team New Zealand beat Dennis Conner 5-0 off San Diego in 1995. The Kiwi skipper then, Russell Coutts, is now CEO of Oracle Team USA.