It looms as the key battleground in the America's Cup match.
The sole upwind leg in the short, five-leg sprint course accounts for 30 per cent of the race, and is where we're likely to see some intriguing tactical battles playing out between Team New Zealand and Oracle, utilising the newest weapon in their arsenal: upwind foiling.
Foiling - when both hulls of the boat lift out the water - has been the surprise development area in the 34th America's Cup. To date, it is something we've only seen the teams do downwind, reaching speeds of more than 40 knots in the process. There were a couple of occasions when Team New Zealand achieved lift-off upwind during the Louis Vuitton finals, but never for any longer than 10 seconds.
Behind the scenes Oracle Team USA have also been working on perfecting their upwind foiling and have reportedly looked very stable.
But so far both teams have been cagey answering questions of how far they have developed their upwind foiling and the prospect of it being utilised in the Cup match.
Team New Zealand skipper Dean Barker said during the Louis Vuitton finals his team had been "playing around" with a few things upwind, but there were big trade-offs to be made.
"The boat is not perfectly set up for foiling upwind; there can be control issues. It's a real balance between angle and speed," he said.
Oracle sailing coach Darren Bundock agreed: "There's a lot of talk about foiling upwind and both teams are foiling sometimes. Sometimes it's best to do it and sometimes it isn't ..."
Luna Rossa skipper Max Sirena has seen plenty of both boats in action and expects to see upwind foiling used as a tactical tool in the Cup match, beginning Sunday.
"I don't think we will see a boat foiling upwind all the time, it's more about tactically how you want to position yourself, and how fast you want to reach the first boundary," said Sirena.
For non-sailing folk, it can be a difficult concept to get their heads around - if the boat goes faster up on foils, why not use it all the time?
The problem is, to foil upwind the boat needs to sail at a larger angle to the wind, and therefore sail a less direct route to the top mark. They might be sailing faster, but they will end up covering a lot more ground and having to throw in more tacks.
Team New Zealand designer Pete Melvin - one of the masterminds behind the AC72 class - said upwind foiling was therefore more likely to be used as means of providing short bursts of speed to position themselves optimally on the race course.
"We're still learning about that and when to employ the upwind foiling mode and trying to make sure we can do it efficiently. Because sometimes you can actually lose a lot of distance very quickly," said Melvin.
The other major problem with upwind foiling, in Team New Zealand's case anyway, is the boat is set up for downwind foiling.
Luna Rossa helmsman Chris Draper said the trim tabs on the rudders were non-adjustable, meaning you had to pick a mode and stick with it, which further explains why the "ruddergate" saga that derailed the opening week of the America's Cup got so heated.
The Italian team also foiled upwind a couple of times during the Louis Vuitton finals but Draper said it was difficult to do stably.
"It's hard to set the boat up to sail well upwind and downwind on the foils. The lifting bit of foil on the rudder, you can't move it while you are sailing. If you could, then you could make that angle increase so you can make the boat level going upwind and have it level going downwind. It has to be fixed for the whole race so we've always fixed it for the downwind."
Draper expects it is a problem the design teams of Team NZ and Oracle have been grappling with in the lead-up to the Cup.