Skuj wrote:
Fischer's age upon winning the US Open.
Karpov's tournament record.
For Fischer, I would say that his US Closed victory, also when he was 14, is more impressive. There have been several 14-year-olds in recent years who have been strong enough to be competitive in that calibre of an Open tournament. After all, several IMs have won or tied for first in the US Open. Even so, given that players seem to reach elite levels and younger ages all the time, I wouldn't rule out someone breaking both records.
Fischer's most impressive feat is his streak of 20 consecutive wins in top-level competition in 1970-71. I don't think anyone will ever match that achievement. Another possibility is his 11-0 score in the 1963 US Championship.
Karpov's 161 tournament victories is also extremely impressive. Karpov, besides being an extremely formidable player, was lucky to be part of a relatively weak generation of players. His main rivals were either from the previous generation (e.g. Korchnoi) or the following generation (e.g. Kasparov).
Mikhail Tal's streak of 93 games without a defeat is also a tough one to beat, but the most amazing thing about it is that it was the ultimate risk-taker, Tal, who achieved it. He also had another 86-game streak.