The matches were hard-fought, but in the end the tournament favorites (at least based on the standings at the end of the preliminary stage) came out on top, and we’ll have a final of #1 Magnus Carlsen against #2 Arjun Erigaisi.
Carlsen’s opponent was the German prodigy Vincent Keymer, and he started well with two draws. In the first game both players had meaningful advantages at various moments before the game finished in a repetition, while game 2 was a calm draw. The match turned in game 3. Carlsen twice had a winning advantage, and twice Keymer fought his way back to equality. The game was close to a draw, but Carlsen kept creating problems for the youngster in a bishop vs. knight ending, and after many, many moves Keymer cracked. A bit like Ian Nepomniachtchi after his loss to Carlsen in game 6 of their World Championship match, the long loss may have broken Keymer’s spirit, and he was completely outplayed and outclassed in game 4. The champion won that game in excellent style to close out the match by a 3-1 score.
The match between Arigaisi and Le Quang Liem could have been even more lopsided, but it wound up going to blitz tiebreaks. Game 1 was a calm draw, but game 2 was a convincing victory for Erigaisi. Erigaisi was (clearly) winning again in game 3, with Black, but he missed his chance and Le escaped with a draw. Having White and draw odds in game 4 wasn’t enough for Erigaisi to finish the match. The opening was fine, but the middlegame went very poorly, and Le won with a brutal mating attack to equalize the scores.
You might expect that Le’s momentum would carry him through in the blitz playoff, but it didn’t happen. The first game was headed for a likely draw when Le chose an active-looking plan that turned his kingside into a disaster zone, and Erigaisi’s attack netted a decisive material advantage that he turned into a win. In the second blitz game Erigaisi achieved an enormous advantage with White, and he found the right idea to make progress, too - except that he found it too late. The piece sac on move 15 was winning; on move 18, when he played it, it left him with the worse position. The resulting position was still crazy, and too difficult for the players to figure out in blitz. The evaluation went back and forth, and in the end Erigaisi’s initiative proved unstoppable, and he won the game and the match by a 4-2 score.
The Carlsen-Erigaisi final takes place over two days, with one four-game set tomorrow and another one on Sunday. For now, here are the semifinal games, with my comments.
"A bit like Ian Nepomniachtchi after his loss to Carlsen in game 6 of their World Championship match, the long loss may have broken Keymer’s spirit, and he was completely outplayed and outclassed in game 4."
A possible interpretation, but maybe it didn't really matter _how_ Keymer had lost game 3, only _that_ he lost it to be in a must-win situation. He had to "take risks" in game 4, and it backfired completely. As often in such situations, games like Erigaisi-Le are relatively rare. Then there's also no need to discuss what is more tiring: a rapid game lasting about an hour with the next game starting minutes later, or a classical game lasting many hours with time to eat, sleep and try to recover before the next game.
"Carlsen refutes the idea at the board" - maybe, but it's also conceivable that he had at least a quick look at the consequences of the white pawn grab before. He had this variation three times before, with black against Artemiev as mentioned in the game notes, with white against Mamedyarov and Dubov. Funny that he had lost with white in rapid against Dubov also due to a bad pawn grab, under different circumstances: 31.Qxa5?? was well in a "middlegame-like (king safety mattered) endgame with queen and one rook for both sides".
It depends on whether 9.Qa4+? is dismissed immediately on human grounds or engine verdict of -1, or whether you check it anyway - being ready for it with black or even checking whether it may still work with white. The entire concept for black also wasn't too different from what black did in the three earlier games.