The Zonal held in Hilversum 1947 was the first Zonal to be held under the new FIDE-run world championship cycle. In 1946, at the first post-war FIDE congress after the war, it was discussed how the world champion should be chosen as Alekhine had died under mysterious circumstances in Lisbon a few months earlier. The congress decided that the world champion would be decided by a match tournament of the six strongest players of the day: Botvinnik, Smyslov, Keres, Reshevsky, Fine and Euwe. Fine declined so the tournament was a 4-game round robin with five players.
At the same time a decision was made on a system of qualifying tournaments which would produce a challenger to the world champion two years after the match tournament. The flaw was that apart from the Soviet Union there was to be only one zonal tournament for all of Europe which meant that the countries with several strong players were at a disadvantage. But at least it was a better system than previously when the title holder, if he felt like it, played a match against whomever could meet his conditions. So, in a very hot July of 1947, the champions of fourteen European countries assembled for the first ever zonal tournament. The right to move on to the next stage went to the first place finisher only. Ties were to be broken by the Sonnenborn-Berger system. Later the number of qualifiers was increased.
When Ludek Pachman arrived in Hilversum he didn't have a lot of international successes on his resume and so had nothing to lose by going for broke which he did by scoring six wins in the first 6 rounds.
In round seven he met O'Kelly and gained the advantage, but was unable to press home the win and had to settle for a draw. At the time nobody could know the effect this draw was to have on the final result.
A win in round 8 left Pachman with an impressive 7.5-0.5 score, but then he lost his next two games putting him at 7.5-2.5. He then regained his winning ways and made up ground by defeating Dr. Petar Trifunovic and Laszlo Szabo.
Going into the last round O'Kelly, who had been playing his usual solid game, and Pachman were tied for first with 9.5 while van Scheltinga and Trifunovic were tied for 3rd-4th a distant 2.5 points back. O'Kelly was playing a tailender, Doerner of Luxemburg, so Pachman knew he had to go all out for a win against the Bulgarian Champion Zvetkov even though he had the black pieces. It wasn't going to be easy because Zvetkov was well known for his solid play even though in this tournament he was badly out of form. And, if Pachman and O'Kelly tied, the tiebreaks favored Pachman.
Zvetkov was at the top of his game in 1956-57. Chessmetrics puts his rating in the mid-2500's, placing him in the top 100 rated players. Alexander Zvetkov (October 7, 1914 - May 29, 1990) was Bulgarian Champion in 1938, 1940, 1945, 1948, 195, and 1951. He represented Bulgaria in four Olympiads.
As expected, O'Kelly beat Doerner, but Pachman lost to Zvetkov.
1) Albrec O'Kelly de Galway 10.5
2-3) Ludek Pachman and Petar Trifunovic 9.5
4) Theo Van Scheltinga 9.0
5-6) Laszlo Szabo and C.H.O'D. Alexander 7.5
7-8) Nicolas Rossolimo and Max Blau 6.5
9) Vincenzo Castaldi 6.0
10) Alexander Zvetkov 5.5
11) Yosef Porat 5.0
12) Kazimierz Plater 4.5
13) Charles Doerner 3.0
14) Bartholomew O'Sullivan 0.5
Pachman included the following game against Zvetkov in two of his books: Modern Chess Strategy (published in 1963) and Decisive Games in Chess History (published in 1972). Curiously, the notes were different.
In Modern Chess Strategy he gave 13...Qb4 a “!” commenting that the Q was actively placed as it would lead to an exchange of Qs should white play Nd5 in reply to ...c5. In Decisive Games he gives 13...Qb4 a “?” commenting that it was not very accurate as demonstrated by white's 14.Nb4.
In MSC he comments that white's best move was 14.g4 followed by Ng3 which initiates operations on the K-side. In DGCH it's obvious from his comment about 14.Nf4 that it was the best move.
In MCS he discusses this 18...Re8 explaining that three moves previously it went to the d-file to counter a possible ...e5 by white. In DCGH he gives 15...Rfe8 a “?” because it soon must return to the e-file.
He also changed his opinion of Zvetkov's 19.g4. In MCS it was given a “?” without comment. In DGCH it was given a “?!” and Pachman said that psychologically his inaccurate play induced his opponent to abandon caution and initiate an attack that was not really justified and that he should have played 19.Nf4-d5 instead.
In both MCS and DGCH Pachman gave his 29...Ne5 a “??” which is correct. He explained that he saw the immediate win with 29...Rxe4, but suffered an hallucination at the last moment thinking that white could successfully play 30.Bxg7. His analysis of 30.Bxg7 turned out to be inaccurate in both books.
In my notes I have decided to ignore Pachman's comments and let Stockfish and Komodo determine the best course of action.