Oracle's recovery from three straight losses a reminder it's about sailors, not just boats.
This was the day human error reasserted itself in the 34th America's Cup.
So far, it's been all about the boats, the technology: which one is faster. Yesterday, it was more about the people who make them go fast - and the mistakes they can make.
Oracle Team USA let what looked like a winning lead slip away in the face of Team New Zealand's upwind speed in Race 3. It looked as if the Cup was quickly moving closer to a journey back to the (protester-proof) trophy case at the Royal New Zealand Yacht Squadron.
But in Race 4, Emirates Team NZ were a little off their game and let Oracle make a confidence-boosting climb back towards zero. Four races - and the score is now 3 to -1.
After Race 3, it was tempting to say the dice were looking loaded. Team NZ's upwind speed looked like that of a Cup winner.
They lost the start, they suffered a go-slow penalty and saw Oracle clear out to an 18s lead at the bottom mark.
And they still won.
It should have been a formality for Oracle. But then began the game of chess that is the upwind leg on this course. Oracle admit their tacking is not as tight as Team NZ's and maybe the pressure got to them.
The mistake can also be laid at the door of Oracle's tactician John Kostecki. At a key moment, they surrendered the right-of-way starboard side to the Kiwis, searching for better current and maybe a "puff" on the left.
Team NZ ramped up their tacking, got the boat moving faster upwind and simply sailed round Oracle to take control.
A measure of that control was that an 18s deficit became a 29s lead at the next mark. In the end, Team NZ won by 28s.
It looked a gut-wrenching, confidence-sapping blow. To have the lead and to have it taken away so demonstratively was deflating indeed. Oracle skipper Jimmy Spithill spoke later about the "huge" effect of not letting the score balloon out to 4 to -2.
But in Race 4, Team NZ made the mistakes. Spithill found his rhythm better yesterday after being outmanouevred on Sunday by Team NZ skipper Dean Barker. Spithill won both starts in a return to form.
In Race 4, he also got prime position for a 6s lead at the important first mark, found some breeze that Team NZ didn't and they were headed for another big lead until Oracle made a daggerboard mistake. It dug the bows in and slowed them from a sprint to a stumble.
Team NZ pulled up to 5s behind and, with the favoured upwind leg to come, four wins looked a distinct possibility.
But Team NZ were not sailing as well; they'd endured a slow gybe or two downwind and their tacking looked more ragged. As Oracle came together smoothly and found a good mode upwind, the Kiwis tried to pull a few tricks out of the bag.
They foiled upwind for a while, the hulls clear out of the water. It looked as if they'd tried for a burst of speed to catch the American boat.
But the bows rose too high, momentum was lost and so was the opportunity.
In the end, Oracle performed the unexpected and won the upwind leg, extending the lead to 16s. The Kiwis rattled home - at one stage finding some pressure that saw them pull back close to the desperate American boat.
But the Oracle team held on for their first victory, by 8s.
So it was an odd day, full of contrary trends. Team NZ were supposed to be the happier team when it blows.
Yet in Race 4, with the wind gusting to the upper limits of the 23 knots allowed in this regatta, Oracle looked more secure and efficient.
Team NZ in Race 3 were so dominant upwind it hurt. But in Race 4, Oracle were more stable and smooth.
It may have been that the New Zealand boat was configured more for the slightly lighter breezes of Race 3 (17 knots-19 knots) or it was just an off-day that will be painstakingly dissected in the lay day today before racing resumes tomorrow.
Mostly, it was a day that reminded all of how hard these 72-foot rocketships are to sail, how easily mistakes can be made, and how the unexpected is never far away.
That was highlighted by a voice, unmistakably Spithill's, when Oracle dug its bows in and slowed hardon the approach to the bottom mark. It could have been a game-ending error.
The voice said: "S***!"