Jenson Button says he feels proud after finishing second in Singapore despite falling ill on the morning of the race.
The McLaren driver is now the only man who can mathematically stop Sebastian Vettel winning the championship.
"I was a kilo and a half lighter than I normally am in the morning," revealed Button, who had to take medication.
"I was good by the race, I managed to get my weight back up, and got through it. I feel very proud I stopped Seb from winning the championship."
Singapore's street track is considered to be one of the toughest on the calendar because high temperatures and humidity coincide with a 61-lap race, which comes close to the two-hour race limit.
A stomach upset made the challenge even harder for Button, who also had to use an ice bag to ease swelling on his left knee after the race.
"I was ill yesterday morning," Button told the Press Association. "I don't know where it came from, but when you do have it you're massively dehydrated.
"So I [took medication], ate a lot of pasta because carbohydrates help you soak up liquid and drank a lot of special drinks from Aki (McLaren team doctor Aki Hintsa), his salty water drinks."
Despite the illness, Button made an attacking start, moving up to second behind Vettel's Red Bull from third on the grid.
The 2009 champion held on to this position through three rounds of pit stops to ensure Vettel cannot clinch a second successive world title until the Japanese Grand Prix on 9 October.
"I feel very proud I stopped Seb from winning the championship in Singapore, that he was unable to celebrate it here, so I'm very happy - but we all know it's going to happen at the next race," Button added.
"I had a goal, from Hungary onwards over the second part of the season, to beat Seb in the points. It's going to be tricky.
"I'm the second highest points scorer so far, and that has to be the aim for the season - to score more points than the others - and hopefully score more points than Seb in the second half.
"But the main aim is to win races. We tried it yesterday, it didn't quite work, but at least I was the closest driver to doing that."