This is the critical position in round 4 at the World Cup between Carlsen and Bareev. Black’s position is basically hopeless. The right continuation would have been:
1. Qf7 Bd2 (1… Ra2+ 2. Qxa2 Nxa23. g7 +-) 2. Ka6 Ra2+ 3. Qxa2 Nxa2 4. g7 +-
Unfortunately, Carlsen played 1. Qf8+??? Kb7 2. Qf7+ Bc7+ 3. Qxc7+Kxc7 4. h5 Rg2 and White resigned.
If he would have won this won position, he would have been in the final 8. What a painful loss for a talented young man. 
Chess Daily News from Susan Polgar
‘Incredible’ is the correct adjective here, but I want to use that for the game of chess ! Chess is so deep..who would have thought that there could be so many possibilities hidden in this position ? I saw this a few hours ago at chessbase, and I was waiting for someone to comment on it. Fittingly it turned out to be you
I was lucky enough to be watching the game on the internet live. well Carlsen was very short of time at this point. I think he only had about a minute for the rest of the game plus his time increment. not sure of the exact time. I am sure he would have found it with a slow game.
I dont feel that Magnus Carlsen lost. I think he has gained incredibly in this tournament. I feel he is maturing and his chess is improving quickly in this tournament. he has really played incredibly well.
Look at the caliber of the people he has been playing against. they are the very best in the world and he has hung right in there.
I personally love his chess and I know he will continue to improve. he is just such a nice kid. I see everyone has been rooting for him. it is incredible. everyone has wanted him to win. what a wonderful testament to Magnus as a person.
Initially I felt like crying when he lost. but then I realized he did not really lose. he is a big winner for playing so well.
I say BRAVO Magnus. Job well done. Keep up the good work. I am rooting for you to still make the next round. there are 2 or 3 places still available. since 10 or 11 of these 16 will continue on.
Susan I only entered the above once and it posted twice with the same time. must be an error in the blog software.
I don’t really blame Carlsen. Qf8+ is an extremely natural move to play, and its not easy to see under time pressure that it leads to a FORCED LOSS ! Chess is a tough game !
It is human to err. Magnus will grow stronger by the loss since adversity builds character.