1990 Kasparov - Karpov Title Match; New York/Lyon, X-XII, 1990
The 21st game of the 24 game match was played on 19 December, with an adjournment the next day. The draw brought the score to +4-2=15 (11.5-9.5) in Kasparov's favor, meaning he needed only a draw to retain the title.
The 22nd game was scheduled for Saturday, 22 December, but Karpov took a timeout. Although there had been pressure from the Lyon organizers to avoid timeouts on the Saturday games (the games were scheduled for Monday / Wednesday / Saturday each week), rumor was that Karpov took a swipe at them for lodging he considered unsatisfactory.
FIDE President Campomanes granted a technical timeout for Monday, 24 December, and the game was played on the 26th. Kasparov got his draw, but the match continued to settle the prize money. This was to be the last World Championship match played using the system of FIDE cycles invented after the death of Alekhine. Before the following title match, foreseen for 1993, the cycle collapsed just after the Candidate matches.
1997 FIDE Knockout Matches; Groningen, XII, 1997
This was the first World Championship using the system of knockout matches imposed by FIDE President Ilyumzhinov. FIDE Champion Karpov was seeded directly into the final match, making the Groningen event more like a Candidates tournament. The 'quarter-final' (second-to-last round) of Groningen was scheduled to have the standard, long games played on 23-24 December, with the tiebreak on the 25th. Anand beat Gelfand in the standard games, while Adams and Short tied with a win each.
In the fifth and last game of their tiebreak, a 5-minutes-to-4 blitz game (now called an Armageddon game), Adams, playing Black, beat Short.
Anand beat Adams in the 'semi-final' (last round), which also reached the Armageddon stage, and earned the right to play Karpov three days later in Lausanne.
- 2000 FIDE Knockout Matches; New Delhi/Tehran, XI-XII, 2000 The final round was scheduled for standard games on 20-26 December (with a rest day on the 23rd) and a tiebreak on the 27th. Anand drew with Shirov in the first game, but won the next three games to win the title of FIDE Champion. It was his first World Championship title.
If my dates are correct, the only games played on the 25th were the Adams - Short tiebreak series in 1997. Anand won the title on 24 December in 2000. In case I've overlooked any events, I'll add them below. In the meantime, a Merry Christmas to one and all!