AWARDCHESS:What do you mean by client?
Part of the reason that Spassky lost to fischer is that he hated being the world champion and stopped playing well. Another example of losing because of underestimation was the Capablanca-Alekhine Match, because Capablanca had never lost to Alekhine before and never prepared for any games anyways (which is why almost all of the games have the same opening), which was the opposite of Alekhine.
Karpov lead Tal 1 or 2 games from about 20, and Kasparov slightly lead Karpov a few games...
Geller VS. Fisher 5:2, as I can recall! It is a best score against Fisher!
Tal first lead Fisher 4:0!
Karpov first lead Kasparov 5:0!
Tal was a client for Korchnoy! As a Bronshtein was been the client for Spassky!
Shirov was been the client for Kasparov!
Fisher first was been down VS. Spassky, before their first Match 3:0 = 2 Draws!
Spassky underestimated him, and paid badly for not enough respect!