The Toksport Skoda driver came down with a stomach bug on the eve of the Safari Rally that marked the start of his WRC2 campaign.
The illness left Greensmith severely sapped of energy ahead of the toughest rally on the WRC calendar. However, the 27-year-old refused to quit and relied heavily on hydration tablets to get him through the rally which resulted in a faultless run to class victory, finishing sixth overall.
Greensmith set the pace from the onset to move into a comfortable lead of more than three minutes at the end of Friday.
Once out in front, he managed his pace after main rival Oliver Solberg dropped almost four minutes following punctures on stages two and three. Greensmith eventually took the victory from Solberg, who also felt the effects of a fever, by 1m23.1s.
"I don't know what I'm more proud of not shitting myself on Friday or actually winning the rally, it has been a long weekend but I'm very happy," Greensmith joked at the finish.
"It's a brilliant way to start the season, the car has been impeccable.
"There was no point that I thought I was going to [give up on the rally due to illness] because I knew I couldn't from my own personal thing.
"Thankfully, I started to get better. We did such a good job on Friday even being ill and it gave us the foundations for it to be easy to control for the rest of the weekend.
"Having a three-and-a-half minute lead is much easier than having to fight but for sure going slowly you can sometimes make mistakes. Whenever we needed the speed, we had it.
"The guys in the team have been saying that is it my best rally there was not a single mistake all rally, so I'm very happy."
When asked if he'd been able to eat much food during the weekend, he added: "I have just been taking a lot of hydration tablets but apart from that not much really."
Greensmith is expected to contest the next WRC round in Croatia (18-21 April) but won't be registered to score WRC2 points.
