Keres USUALLY played poorly and passively against Botwinnik in 1940-1950s
See Chigorin's memorial 1947
http://www.chessgames.com/perl/chessgame?gid=1032154
USSR championship 1952
http://www.chessgames.com/perl/chessgame?gid=1032264
This is more akin with psycological pressure that Lasker put on his opponents (who all underperformed against him) than with any political coersion.
Part 1 is here: http://www.chess.com/forum/view/general/examples-of-soviet-cheating-in-fide-competition-keres-botvinnik-1948
Part 2 is here: http://www.chess.com/forum/view/general/soviet-cheating-n-fide-competition-keres-botvinnik-1948-pt-2
Part 3 is here: http://www.chess.com/forum/view/general/soviet-cheating-in-fide-competition-keres-botvinnik-1948-pt-3
This is the conclusion - The Championship moves to Moscow.
After the first two legs at the Hague, Botvinnik led with 6 points in 10 rounds. Reshevsky of the USA was second, with 4.5 points. Keres and Smyslov had 4 points each, but Keres has beaten Smylov twice. Euwe was out of contention with 1.5 points.
The championship entourage boarded a train for the trip to Moscow. Grandmaster Hans Ree, in the Foreward to the reprint of Euwe's book on the 1948 Match Tournament, related how when the train needed to clear customs at the Soviet border, guards there seized Euwe's personal papers (which contained his opening analysis). Their intent was to send the papers to Moscow for "review" by the authorities. Euwe was already having a bad tournament, and this incident must have affected him.
As it was, Botvinnik placed a telephone call to Moscow, and the papers were returned to Euwe, after he signed a document disavowing any ill intent to the Sovet Union.
The Soviet Sports Committee was very concerned about Reshevsky. Sammy had blown a win against Botvinnik in the first round, and lost in time pressure. Their second round game was a draw.
GM Boris Gulko, in "The KGB Plays Chess" (pg 8), states that the Soviet authorities were planning contingencies:
"Did the government make it easier or harder for Botvinnk to win? Evidently, it did both. In the middle of the 1948 world championship tournament, which brought Botvinnik to the world title, the grandmaster was summoned to a meeting of the Secretariat of the Central Committee of the Communist Party. Andre Zhdanov, one of Joseph Stalin's closest collaborators, told Botvinnik:
"We are afraid that Reshevsky (the great american grandmaster) will become world champion. How would you like it if the Soviet participants lost to you on purpose?"
"I lost the ability to speak," Botvinnik recalled, "Why did Zhdanov have to humiliate me? When I regained the ability to speak, I categorically rejected his offer."
Naturally, such an upheaval coould not has passed without any effect, and Botvinnik lost his next game in the tournament - against none other than Reshevsky.
Reshevsky's win would set up the most controversial game of the tournament - Keres versus Botvinnik in Leg 3.
Numerous reports suggest that Keres was upset when he arrived for the game. He played a line, as White, that divirged from his previous sucesses against Botvinnik. Indeed his play was solid and unspectacular - odd for a player still in the thick of the championship chase.
This infamous game is recorded here, with 8 pages of commentary. I urge the reader to come to their own conclusion: http://www.chessgames.com/perl/chessgame?gid=1032191&kpage=1
British champion, Harry Golembek, revealingly wrote,
"One had to rub one's eyes in incredulity at the sight of Keres committing such obvious positional errors...His play was inexplicably weak...as though he was determined to lose."
Keres was considered one of the top endgame technicians. Indeed, I own one of his endgame primers. What happened to him at Move #53? Indeed, why did he play so poorly after both the first and second adjournment?
Golembek may have hit the nail on the head. It appears to me Keres had been coerced, and needed to make a loss look reasonable, without being obvious.
Grandmaster Larry Evans felt Keres "threw" the game, disbelieving that a player of Keres' magnitude could possible botch that endgame.
Reshevsky himself was suspicious of Soviet behavior:
HANNON W RUSSELL: What did you feel your chances were going into that tournament?
RESHEVSKY: I didn't know because there was a question of how the Russians were going to play against each other.
HWR: Even then?
RESHEVSKY: Even then. There was this rumor, unconfirmed, that the Russian threw games to each other, if necessary.
HWR: Do you think that happened in 1948?
RESHEVSKY: I had a suspicion that it might have.
HWR: But Botvinnik won that tournament going away.
RESHEVSKY: Yes, I know, but I had my doubts.
GM Hans Ree, was more direct:
"The diagram presents the case that seems most convincing to me. Keres has an easy draw with 50 Ra4 but found an idiotic plan to put his healthy rook into the most passive position. You cannot call it a mistake."
I think here, the preponderance of the evidence suggests Soviet machinations at work. Keres would lose the first four games to Botvinnik. When they met for the fifth time, on the last round, Botvinnik had already secured the title.
Keres, years later, related to Wolfgang Unicker, that in the last game, Botvinnik offered Keres draws at Move #5 and Move #12. After the second offer, Keres said that he told Botvinnik to go screw himself! (paraphrased) ;^)