Panno resigned after Fischer played 1. c4.
And it was Interzonal tournament!!!
He had no hopes of winning the shot into the Candidates.
Larry Evans, who was present explained:
"Essentially, it was a protest by Panno. Games normally started at 4:00 PM, but Fischer and Reshevsky had a special dispensation to begin games played on Saturday at 7:00 for religious reasons.
Panno did not feel this was fair; especially in the final round, with qualifying spots for the Candidates matches still up for grabs, he felt all games should start at the same time.
Hence he didn't show up at the board. Fischer plays 1.c4 and actually went to find him, not wanting to win on forfeit. Panno eventually came to the board, but only to officially resign."
On a related note, from Wikipedia:
"The shortest game ever lost by a grandmaster because of the position on the board was by future world champion Viswanathan Anand, who resigned on move 6 against Alonso Zapata in 1988 (1.e4 e5 2.Nf3 Nf6 3.Nxe5 d6 4.Nf3 Nxe4 5.Nc3 Bf5?? 6.Qe2 winning a piece, since 6...Qe7 is answered by 7.Nd5 Qe6? 8.Nxc7+)."
Here's that game as a study: lichess.org/study/oGzcz0ZR
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