The world chess championship currently underway in Dubai is not over officially, but for all intents and purposes it may have been decided already.

After a string of five draws to begin the championship, Magnus Carlsen, the reigning champion from Norway, has won two of the last three games, to take a lead of five points to three over his challenger, Ian Nepomniachtchi of Russia. Each victory counts as one point in the best-of-14-game match. The first player to reach 7.5 points will be the winner.

Carlsen’s position in the match is akin to having a 10-meter lead in a 100-meter race, with less than 50 meters to go. Or, given the length and speed of elite chess, like having a one-mile lead at the halfway point of a marathon.

Either way, it would take a historic stumble by Carlsen to keep him from retaining the world title he first captured in 2013.

The breakthrough that blew open the contest occurred Friday in Game 6, an epic struggle that rewrote the chess record books.

The game lasted 7 hours 45 minutes and consisted of 136 moves, making it the longest game in world championship history. Indeed, it went so long that the game actually ended Saturday morning, just after midnight, local time.

In Friday’s game, Nepomniachtchi, perhaps feeling ambitious, avoided a chance to exchange queens in the early going, which most likely would have led to another draw. Then a few moves later, he allowed Carlsen to trade his queen for both of Nepomniachtchi’s rooks, leading to a double-edged but dynamically balanced position.

Uncharacteristically, though, Carlsen got into time pressure at several points and had to scramble to make several moves to avoid forfeiting the game. (The players are required to make their first 40 moves in two hours. If they fail to do so, they lose.) During the scramble, he missed a winning opportunity found by computers analyzing the position.

For most of the rest of the game, Carlsen and Nepomniachtchi were not only trying to solve problems posed by their opponent, but also doing so at times with only a minute or two left on their clocks to make their decisions.

Gradually, Carlsen gained the upper hand. On Move 116, an endgame arose where Carlsen had a rook, knight and two pawns against Nepomniachtchi’s queen. Though the game could still have ended in a draw, fatigue took its toll and Nepomniachtchi did not find the correct moves. Nepomniachtchi resigned as it became clear Carlsen would win.

Game 7 ended in a relatively quiet draw, with neither player having any real chances to win.

In Game 8 on Sunday, Nepomniachtchi again was playing Black, or second, as he had in his first defeat. He played aggressively in the opening, eschewing a chance to trade queens early on and also not castling his king, which is the usual method to keep it safe. Despite those decisions, the game remained balanced until Move 21, when Nepomniachtchi made a serious error, losing a pawn.

Perhaps unnerved by his mistake, Nepomniachtchi struggled to put up a stiff resistance. Carlsen soon won a second pawn and then began to advance his pawns up the board. Nepomniachtchi, trapped in a hopeless position, resigned on Move 46.

In the news conference afterward, Carlsen said he believed Nepomniachtchi’s decision to play aggressively in Game 8 and his mistake were caused at least in part by his loss in Game 6 and how that had put him in a hole in the match standings.

“This second win probably does not happen without the first,” Carlsen said. “Everything is kind of connected.”

Nepomniachtchi, who “apologized” for his performance, was left to face a dire position on Monday’s rest day: There are only two previous cases in a world chess championship in which an opponent has successfully overcome a two-game deficit.

The first was in 1935, when Max Euwe trailed Alexander Alekhine by such a margin after four games. But Alekhine was an aging, overconfident player with an alcohol problem at that point in his career, and the match went 30 games, giving Euwe enough time to recover. He won, 15.5-14.5.

The second example was in 1972, when Bobby Fischer lost the first game of his match to Boris Spassky and then forfeited the second. Fischer was clearly the superior player at the time, however, and he stormed back to take the title, 12.5-8.5.

Nepomniachtchi, who was the underdog to Carlsen before their match, has a similarly big hill to climb and not many games left to do it.

Asked after Game 8 about his chances to retain the title, Carlsen replied quickly and with a faint smile, “They are very good.”