The Madness of the World Chess Championship

So after three weeks and 12 indecisive games, reigning champion Magnus Carlsen of Norway and challenger Fabiano Caruana of the U.S. are heading to overtime. It’s the first time ever that regulation play hasn’t produced a single victory for either player. Carlsen and Caruana will return to the board one more time on Wednesday for a series of fast-paced tiebreaker games.

“We both had our moments,” Caruana said. “I actually wouldn’t mind more rounds. Sixteen or 18 rounds would be fine.”

Inside a fishbowl of soundproof glass in London, the past three weeks have delivered nonstop mental and physical theater. Caruana is trying to become the first American champion since Bobby Fischer in 1972, while Carlsen is hoping to burnish his legacy as one of the game’s all-time greats.

The match reached overtime after a series of bizarre events not normally associated with the word “chess.”

Before Game 4, a snippet of footage showing Caruana’s preparation leaked online, and the chess universe caught fire: Would it provide an undue advantage for Carlsen? Was it a gambit of misdirection from Caruana’s team?

But before those questions were resolved, Carlsen arrived for Game 9 with an unexpected problem of his own: a bandage above his right eye. The injury was not chess related—no bishops were hurled in his direction. Instead, the player who achieved the highest Elo rating in chess history had spent his day off playing soccer and collided with a Norwegian journalist.

Carlsen did not suffer a concussion as initially feared and was cleared by his medical team. But his mental acuity was thrust into question after the game when a poor move allowed Caruana to draw against him. Carlsen, afterward, conceded he “blew it.”

Then in Game 11, an opening that Caruana was shown in the video preparing for—known as “Petrov’s Defense””—emerged on the chessboard. Everyone knew Caruana had prepared for this. Which made it seem only more likely that Carlsen had seen something he could exploit in the video and was now baiting Caruana into it. Nonetheless, the game finished in a draw.

That set the stage for the potentially climactic Game 12. Carlsen was playing the black pieces, which move second in each match and theoretically begin on the defensive. Yet after 21 moves, top experts and sophisticated chess computers agreed that Carlsen held a significant advantage. As the match proceeded, chess computers showed that Carlsen could have turned the screws even further with a single move and put himself in position to snatch the game and the title.

Despite his decided edge, however, Carlsen abruptly proposed a draw. The pleasantly surprised Caruana leapt to accept it. On the other side of the glass, the chess world fumed.

“I’m very shocked by Magnus’s decision,” American grandmaster Hikaru Nakamura said on the chess.com broadcast.

Caruana didn’t conceal his relief. “I was down a lot of time and had a position I didn’t really feel comfortable with,” he said. Asked afterward what he thought of a move that pushed his edge, the champion of the most logical game on earth didn’t have a logical answer. “I don’t care,” he scoffed.

Now the two grandmasters are headed to tiebreakers. First, they will play four “rapid” games, in which the two players begin with 25 minutes on the clock and get a 10-second increment after each move. If that does not produce a winner, they will play blitz games, in which the players get five minutes and a three-second increment.

If those games fail to produce a winner, the championship has only one solution: Armageddon.

That’s the name chess gives to its most extreme tiebreaker. It has never been used to decide the world championship. It has rules so arcane that the chess world might actually descend into anarchy if it becomes necessary. But it has a necessary function. It is guaranteed to produce a winner, if not the end of the world.

Players draw lots to pick sides. Then, white has five aggregate minutes to complete its moves and black has only four. Here’s where it gets even wilder: If the game ends in a draw, black wins.

“Let’s hope there won’t be Armageddon, because it’s a little bit too much,” grandmaster Sergey Karjakin said before losing to Carlsen in tiebreakers at the 2016 world championships.

Turbo-charged tiebreakers can be a gruesome way to settle three weeks of carefully considered competition and many experts argue that they aren’t in the spirit of elite-level chess. But the alternative is a scenario like the 1984 World Chess Championships between Garry Kasparov and Anatoly Karpov, which dragged on for 48 games over five months without a winner. The president of chess’s world governing body ultimately ordered the match to be abandoned due to concerns over the players’ health. Karpov had reportedly lost upwards of 20 pounds.

Wednesday’s proceedings will be significantly shorter.

Historically, Carlsen is the stronger rapid and blitz player—he is No. 1 in the world in both formats with a sizable rating advantage over Caruana. And experts believe that his intuitive style could throw the more calculating Caruana, who has faced time crunches already in this championship, off-balance. That said, shorter formats introduce an element of randomness—there is no time to correct for mistakes. Even the worst team in the NBA would like its chances in a five-minute overtime against the Warriors better than its chances of winning in regulation.

“I think I have a very good chance, obviously. But I don’t know what’s going to happen,” Carlsen said. “Before today, I thought getting a tiebreak would be getting a good result.”

Before Monday, it also seemed like the tiebreaks could be a formality. But Carlsen’s shocking decision to offer a draw in Game 12 has the chess world wondering about his mental state.

“Tiebreaks require tremendous nerves,” Kasparov tweeted. “And he seems to be losing his.”

Write to Andrew Beaton at andrew.beaton@wsj.com and Joshua Robinson at joshua.robinson@wsj.com