The three-time Olympic champion's day took an unexpected turn when a collision on the startline left him dashing to shore in search of a replacement boat after his sustained damage.
On finding one and switching his own rig into the spare hull, the 35-year-old managed to make it back out in time to start the second race, in which he finished third to amass an unassailable 35-point lead ahead of the final ten-boat double points-scoring medal race on Saturday.
"It was one of those crazy days and a really strange pre-start incident I think because of the big waves and trying to clear another boat which would have caused me to capsize onto another boat," said Ainslie.
"I injured myself in the process and reasonably damaged my boat so there was no real chance of continuing in the race in that state, so the best option was to come ashore and luckily there was a spare boat lying in the dinghy park that no-one was using.
"So we just switched the rigs round, came back out and just had to try and get a reasonable race to get round the course.
"As it turned it out I was not very quick at all but managed to sail reasonably well and had very good speed downwind and I finished third.
"So it was a bit of an epic day, but sometimes these things are sent to test you and in a way there were actually some good lessons learned from crisis management."
Ainslie, who defends his Princess Sofia crown from 2011, was particularly delighted with his dominant performance following a testing winter, during which he underwent surgery for a back complaint.
"It's a real boost to win here after a very difficult period so I'm very happy with the way I've been sailing and things in general, and my body seems to have held up reasonably well," he added.
"I'm happy but there's a lot of work to do yet in the coming months in the build-up to the Games, and I'll keep pushing to try and get better and be better prepared."
Meanwhile, Helena Lucas enhanced her Paralympic selection hopes with a silver medal in the 2.4mR class behind Holland's Thierry Schmitter, with British team rival Megan Pascoe back in sixth.
"It's great to get a silver medal here – it just gives you that boost of confidence going into the next regatta," said Lucas.
"It's a really strong fleet and it's great to go up against those guys and come away knowing I've got really good speed in all conditions, so I've been really happy with how the week's gone.
"Obviously I'd have liked to have been a bit closer to Thierry and given him a bit more of a run for his money. It looked like it was panning out that way at the beginning of the week but he kind of found his stride disappeared off into the distance a little bit but I'm not too worried about it.
"I know I'm going pretty quick against him and he had one of those regattas where he couldn't really do anything wrong. I'm pretty confident I'm snapping at his heels, and going well all round."
