I don't count games from simuls, no. Although he played it against Karpov in an Exhibition Game on TV, which is also dubious. Of course for an Exhbition Game, being entertaining is more important than the result. And the quicker the time control the better the King's Gambit is.

<Unlike Evans, which is just about giving up a Pawn for quick development with attacking chances in open position, KG's main idea is strategic, not tactical.>

Mmmm, it depends which variation Black plays. There are certainly variations like you describe, but not all of them.

<But in my humble opinion it is playable even in correspondence play, and in otb it can be very dangerous weapon in hands of a player, who understands it. Spassky was definitely one of them.>

Definitely playable, just not the best line. But there are equalizers. One of them, as you say, is who well each player understands it. Another is how well prepared each player is for it.

Is it likely he will have extensive knowledge of the variations of the Kings Gambit?

Thanks for the vote of confidence <kp>, but don't believe everything <tpstar> says - ha!

Whereas I have a knack for picking interesting tactics, and perhaps even naming mating patterns, I think I'd go with <perf> and <fsr>'s opinion over mine for practical play.

No doubt some do, but I don't think it's a given. The King's Gambit is a rarity, so I'm sure some GMs aren't well prepared for it. Joe Gallagher wrote a book on it, in which he said that a lot of strong players weren't ready for it, including GM Barczay, who lost to Gallagher's King's Gambit in 14 moves! J Gallagher vs L Barczay, 1990. Gallagher has quite a few short wins with the King's Gambit, most not against grandmasters, of course. https://www.chessgames.com/perl/che...

Spassky is the greatest King's Gambit player ever. Just look at his record. It is extraordinary, including wins against Fischer, Karpov, Bronstein, Portisch . . . https://www.chessgames.com/perl/che... Some of those were from bad, or even lost, positions! It shocks me that Seirawan didn't anticipate that Spassky would play it. Neither had Fischer at Mar del Plata 1960, but this was 25 years later. And the Candidates is kind of an important tournament, so you expect a high level of preparation.

The King's Gambit is a bad opening. Jan Gustafsson likes to observe that 2.f4 is White's 23rd best move (out of only 28 possible)! White is much worse after just two moves, yet Seirawan managed to be much worse after Black's sixth move!

My original supposition was that Seirawan was simply ignorant of KG opening theory and improvised at the board, with disastrous results. But that's not the case. Seirawan writes in "Chess Duels: My Games with the World Champions," p. 153:

<The King's Gambit! Talk about catching me flat-footed. Of course, I knew that Boris did, on occasion, play the King's Gambit, but somehow I had put it out of my mind and out of the realm of possibility.>

Seirawan then relates that he'd had a blitz session with Robert Byrne, who liked the King's Gambit, "and I had come off pretty well in those games." He continues:

<The line I liked best for Black went 3...g5! 4.h4 g4 5.Ne5 d6 (much attention had also focused on 5...Qe7 6.d4 d6) 6.Nxg4 Nf6 7.Nxf6 (7.Nf2 Rg8 8.d4 Bh6 looks fine for Black) Qxf6 8.Nc3 Nc6! 9.Nd5 Qg6 10.Qf3 Nd4! 11.Nxc7+ Kd8 12.Qc3 Qg3+ 13.Qxg3 fxg3 14.Nxa8 Nxc2+ 15.Kd1 Nxa1, with a typically scrappy kind of position that I'd more or less analyzed out to a draw.>

But, Seirawan continued, he and Jacob Yuchtman had once done some superficial analysis of 3...Ne7, a move Yuchtman liked. Yasser explains:

<somehow right now it seemed to fit the bill for taking the game off the beaten track. I hoped to catch Boris off guard.>

FWIW- <Caissabase> gives 3...Ne7 a scoring score of only 37.4%, the lowest score of any of Black's options.

By the way, I've never heard anyone but me comment on Fischer's strange about-face on the King's Gambit. Spassky shocks him with it at Mar del Plata 1960, gets a worse game from the opening, but outplays Fischer and wins. A year later, Fischer's famous article <A Bust to the King's Gambit> is published in the first issue of Larry Evans' "American Chess Quarterly." Fischer modestly opines, "The King's Gambit is busted. It loses by force." Fischer only covers 3.Nf3 in the article, but concludes, "Of course White can always play differently, in which case he merely loses differently. (Thank you, Weaver Adams!)" https://en.wikipedia.org/wiki/King%...

Cut to the U.S. Championship of 1963/64. In Round 2, Fischer faces Larry Evans, whom he had never beaten. Fischer plays . . . the King's Gambit! Imagine Evans' shock! But Fischer plays 3.Bc4. Evans is unable to determine how White "merely loses differently," and is crushed. Fischer vs Evans, 1963. Fischer goes on to win the tournament 11-0.

Fischer annotated the game for Chess Life. He just says of his second move, "I knew that my opponent had some prepared line (since he usually plays the Sicilian) but felt that he would be unfamiliar with the King’s Gambit. Besides, I'd made up my mind to play it in this tournament anyway." He says of 3.Bc4, "Better than 3.Nf3 which is practically refuted by 3…d6 (see my analysis in the American Chess Quarterly.)" https://gambitchessplayer.com/2019/... Whatever happened to "The King's Gambit is busted. It loses by force." and "White can always play differently, in which case he merely loses differently."? Did Fischer believe that at the time, or did he just say it to sell magazines?