Regarding Spassky-Karpov, let's just say that Spassky's sudden loss was rather convenient for Karpov.

That could be because you hang mostly around Americans. I've lived in Germany and other areas, and have heard as much on the other side. (Think Lt. Surena, but with more marbles and less nastiness).

But the theory goes that it was very suspicious that Saidy should blow the draw on the very last move he cold plausibly do it (the sealed move, right before he'd have a whole night to analyze the game). The presumed motive is that people were upset that America's only world championship hope seemed semi-retired after Curacao, and what better way to snap him back in than with a shutout win? (The fact that Saidy and Fischer were friends doesn't hurt).

As for Fischer's 11-0 sweep, I'll concede that Petrosianic does raise a couple of interesting points. To be honest, I'd not thought of the fact that Fischer was pretty inactive during 1963---thus, that shutout just might have sparked something in him.

As for Spassky's "never (would) have thrown a game", well, maybe Spassky wanted to keep himself in good standing with the Soviets, but who knows ?! It's worth repeating that the Spassky-Karpov game took place in the last round, and thus, the result made a big difference to Karpov.

In other words, if the game had occurred earlier in the tournament, then it would not have looked so strange.

I recall that Tal was also accused of losing games on purpose, to Karpov (Bugojno 1980) and to Kasparov (Brussels 1987) - the latter a last round game that enabled Garry to catch Ljubo. Frankly I think such accusations are usually malicious.

That Karpov (or any other GM) could sometimes wear down an older opponent in a drawn endgame by sheer attrition is not surprising. A notorious example:-

Most interesting; I had never heard this regarding Tal in any fashion till now.

In that connexion, does the actual course of Karpov vs Tal, 1980, as the sole decisive result between these titans in twenty games of classical play, disprove such an accusation, or lend weight to it?

<....Frankly I think such accusations are usually malicious.>

Jan Timman wrote about Bugojno 1980 in one of his books "Studies and Games" (a translation of 1983's Schaakwerk I) and I quote:-

Even though he hadn't formally defected, Spassky had left the USSR for good in 1977. A year after this game Spassky broke decisively with the USSR because, he said, they were favoring Karpov. Nothing is impossible, but I would be stunned if he threw this game to someone he really didn't like.

That would involve the sequence 10. Nc3-e2-g3-f5-e3-18. Nc4, I suppose. For defending a weak doubled b-pawn... so I would have made 6 (...) kinda useless Knight moves in 9 moves.