McLaren driver Lewis Hamilton says winning the drivers' championship will now be difficult after failing to gain any points in Singapore on Sunday.
Britain's Hamilton crashed out after a collision with Red Bull's Mark Webber, making it the second consecutive race in which he has failed to score points.
"Twenty points is a massive gap with four races to go. I have to hope for something," Hamilton said.
"But the points gap is just a race victory away. It's not insurmountable."
Hamilton had run third from the start behind eventual winner Fernando Alonso's Ferrari and Sebastian Vettel's Red Bull, but was passed by Webber when he made his pit stop for new tyres.
The Englishman tried to seize an opportunity to overtake the Australian after he got caught up by two backmarkers.
But as Hamilton tried to pass on the outside, the two collided and Hamilton's race was over.
"I saw Mark made a mistake and got caught by a backmarker so I knew I could slipstream him into Turn Seven and I thought I was enough past him," said Hamilton.
"After that I'm not really sure what happened, he was in my blind spot, I didn't see him alongside me, next thing I know is my tyre's blown and that's it," said Hamilton. "I'll have to watch it on TV and see what really happened."
[With not finishing at the previous Grand Prix in Italy] I couldn't have had a worse two races at this time of year. Hopefully myself or Jenson can still win the world championship. I have to get my head down and hope for something."The 2008 world champion's failure to score any points leaves him trailing Webber, who now holds an 11-point advantage from Ferrari's Fernando Alonso, who won Sunday's race.
Hamilton is third in the race with 182 points, while Red Bull's Sebastian Vettel in fourth on 181 and Button fifth on 177. The top five drivers are still separated by just a race victory.
But while Hamilton refused to point the finger of blame at Webber, McLaren team principal Martin Whitmarsh was left with no doubt were the blame should lie.
"We are not here to attack Mark Webber," Whitmarsh said.
But at the point of the incident Lewis is legitimately in front, he left space, in hindsight he should have left more, but it was not reckless and he was unlucky to come away like he did. Mark was lucky to get away with it."Fernando Alonso's victory in the first of the five deciding races of the season has fundamentally altered the dynamics of the title battle.
Following the collision the stewards investigated the incident but deemed that no blame should be attached to either driver.
For Hamilton the incident brought back memories of his crash in Monza two weeks ago where he was forced out of the race on the opening lap following a collision with Ferrari's Felipe Massa.
"I think Lewis is a great driver," added Whitmarsh.
"Two weekend's ago he took too great a risk and he knows that. But today he was unlucky with what happened. He is very disappointed.
"Mark is a robust driver and he has made a few robust manoeuvres. There are four races left and we need to look forward."
Webber himself was lucky to come away from the incident unscathed, although pictures of his front tyre after the race showed how close he had come to having to retire himself.
But with four races left, the Australian is now edging closer to his first world title.
"It was a key part of the race, it was important that I kept him out," Webber said.
"It was the same as Monza for Lewis and I could easily have been out, and there was contact.
This can happen sometimes, we brake completely on the limit. For sure it was incredibly tight - we did not hit that hard, but enough to probably put both of us out of the race. Fortunately I could continue."It's not something you want to do all the time."
Red Bull team principal Christian Horner also defended his man, simply calling the collision a "racing incident."
Meanwhile, world champion Button who finished fourth on Sunday also admitted that failing to earn a podium finish seriously dented his chances of defending the title.
But the Brit has vowed to fight to the finish in all four of the remaining races.
"When you can't catch a Red Bull that has 30 more laps on its tyres [Mark Webber] it shows how quick they are," Button said.
"But we go to Japan happy, we have a good upgrade for that race. We wanted to have it here but couldn't because of reliability issues.
I am still in the title race, it's a very small margin and we will race until the last race. There is everything to play for."Lewis' incident shows that consistency is important, but I need to be on that podium."
Alonso said: "It remains very tight. All five contenders still have the same possibilities.
"Mark has a little bit more with still some margin to have a bad weekend not putting at risk the contention of the championship.
For the others we need to keep catching if we can. We will do our best. We do not know if it will be enough to become champion in Abu Dhabi."But we will give 100%. Hopefully it is enough but people can be sure we will fight until the end."
