In a comment to my post on The Vladimirov Affair, Michael Goeller wrote,
An interesting case of match-second-betrayal I recall was Geller's (likely Soviet-ordered) betrayal of Spassky before the 1974 candidates match with Karpov. Byrne (who lost a quarterfinal match to Spassky) documents this very well in his NY Times book on the matches.
Since I wasn't familiar with this story, I immediately obtained a copy of Byrne's book. In his chapter on that 1974 candidates semifinal, Byrne introduced the match with the following paragraphs.
It was a terrible blow for [Spassky] to learn that Efim Geller, the brilliant opening analyst who had worked with him on the championship match in Iceland [vs. Fischer 1972], had now gone over to Karpov's camp. It is difficult to understand how the Soviet Chess Federation could permit such a move, which allowed Spassky's deepest secrets and opening plans to be turned over to his opponent.
Spassky did make some attempt to accommodate himself to the dismal situation by trying defenses that run counter to his classical style, namely the King's Indian Defense of game 3 and the Dutch Defense of game 7. However he played like a duck out of water and was lucky to give up only 1 1/2 points in the two games.
Moreover, Spassky played do-nothing continuations against Karpov's Caro-Kann Defense in games 2, 4, and 6, undoubtedly fearing unpleasant theoretical surprises. Fighting a match like this with blunted weapons would be too much for anyone, but why didn't Spassky begin earlier and work harder on enterprising alternatives to the openings Geller knew him to favor?
Spassky is a fascinating personality, a mixture of strange contradictions. He told me afterward that after his easy win in the first game he became so overconfident that he could not concentrate for the rest of the match. But how could he reconcile that with his worry over Geller's fine opening work? Could he have been excessively optimistic and scared skinny at the same time? ('Anatoly Karpov: The Road to the World Chess Championship', p.81)
What did Karpov have to say about Geller's help? In 1980, co-author Aleksandr [Alexander] Roshal quoted Geller in a brief account of pre-match preparations.
It had been noted that, as regards the openings, Spassky did not prepare very thoroughly for matches, and so it was decided to adopt against him as many different unexpected schemes as possible. In order to successfully adopt such tactics, Karpov had to undertake an enormous amount of preliminary work. It is sufficient to recall that Efim Geller, an openings expert, wrote:"As regards versatility, Anatoly Karpov is inferior to his opponent. This is noticeable, in particular, in his limited opening repertoire. As White Karpov plays only 1.e4 and as Black sticks to one or two defenses..."At that time Geller had not yet become Karpov's second trainer, and could not have known that the young grandmaster was not at all what he appeared to be. Spassky judged Karpov exactly as Geller did -- and was wrong. ('Chess Is My Life', p.137)
There is nothing else about Geller during the match itself. He first appears as one of Karpov's seconds for the final candidates match against Korchnoi. 'Karpov on Karpov' mentions a few anecdotes related to Geller, but nothing on the 1974 match with Spassky. I've already used the same source for a post on The 'Clear Head' Theory, a first hand account by Karpov on Spassky's style of opening preparation.
Kasparov echoes much of the above in his summary of the match preparation. In the more than 30 pages he devotes to the match, there is no mention of Geller's contribution to Karpov's team.
The Spassky - Karpov match was that epochal event, after which the enormous significance of opening proficiency became clear to everyone. Spassky prepared for the match in the old fashioned way, and this method proved inadequate, quickly leaving him effectively 'without an opening'. Whereas, by contrast, for two and a half months Karpov and his trainers polished their planned opening systems, studying not so much variations, as the conceptual fundamentals of opening lines, their middlegame and sometimes their endgame positions. Karpov worked for 10-12 hours a day! Spassky had no conception of the strength of the grandmaster against whom he had been drawn.
On this occasion Karpov was helped by Furman and Razuvaev (there was no Balashov: Spassky had turned to him for help, not knowing that he was in the opponent's team, and Yuri decided to observe neutrality). Two major surprises were prepared: with Black, the Caro-Kann Defense, and with White, a partial switch to 1.d4. ('My Great Predecessors V', p.249)
What to conclude here? The Soviet sources don't confirm Byrne's account and they provide an alternate, plausible explanation of Spassky's difficulties in the match. Is that because Byrne got it wrong -or- because the subject is awkward for Soviet insiders?
Byrne mentioned that he discussed the Karpov match with Spassky in person. It's a pity that Spassky has written nothing about his many key matches. He would be the best witness to explain what really happened.