Several prestigious events are underway, so it’s time to do a little catching up. Let’s start with an event that I mentioned a few days back, the Women’s Candidates. As with the open (“men’s”) version, it’s an eight-player contest whose winner will face the World Champion (the Women’s World Champion in this case), but in almost every other way the two events are different. The Candidates was a double round-robin, with everyone playing at the same time. The Women’s event, by contrast, is a series of knockout matches, with first one group of four playing down to a single finalist and only once that’s over will the second group of four have their matches. And then? Not until the first quarter of 2023 will the two winners of their four-player groups face off in a six-game match to decide the next challenger for the Women’s World Championship.
I’m not a fan of the format (at least of the staggered, gappy schedule), but it’s an experiment; maybe it will prove successful. There’s no complaining about the drama of the quarterfinals, though, at least for the match between Humpy Koneru and Anna Muzychuk. While the Tingjie Lei-Mariya Muzychuk match finished fairly routinely - Lei won game one and drew the next three to advance - the Koneru-Muzychuk battle had a bit of everything. Koneru won game 1 and drew the next two games to reach the cusp of victory. Muzychuk had to win in game 4 to push the match to a playoff, and of course she did it, grinding out a win against the Petroff.
On to tiebreaks, starting (and as it turned out, finishing) with four rapid (15’+10”) games. The first two games were clean draws, and then the drama began. With White in game 3, Muzychuk obtained a serious advantage after the opening, and was soon winning. But it was a very tactical and unbalanced position, and the players took turns making errors. Generally the shifts in evaluation went from White having a winning position and then slipping to a small edge, but when Muzychuk missed a couple of her opponent’s ideas it was Koneru who suddenly had a winning advantage. Prosperity didn’t last for her, either, and soon Muzychuk was winning again. Koneru launched a desperate counterattack that forced her opponent to find and work out a deep idea, and given the short time control Muzychuk was unable to do it. She ultimately chose safety, and the game was drawn.
And then…a remarkable final game. With the match still level and Muzychuk playing Black, you’d expect something solid. She is a former women’s world champion in blitz, so you wouldn’t expect her to do anything crazy to avoid the next set of tiebreakers (a pair of 5’+3” games, and then a pair of 3’+2” games if necessary, followed by sudden death 3’+2” games). So what does she do? She trots out the Von Hennig-Schara Gambit! The old interpretation would have been insane to play in such a game, but there have been some new ideas lately, and they’re good enough to make this risky without spilling into lunacy.
The players cranked out 15 moves of theory, and then Koneru…blundered a piece, missing a simple three-move line. Muzychuk did not miss her chance, and Koneru resigned immediately. It’s a tragic way to be eliminated from the Candidates, but all credit to Anna Muzychuk for winning on demand in game 4 and for having the guts to play this gambit in game 8.
Coming to the present, the semi-final between Anna Muzychuk and Tingjie Lei is at the halfway point. Their first two games were drawn, today (Thursday) was a rest day, and the last two (classical) games will be Friday and Saturday, with tiebreaks (if necessary) on Sunday.
Games 4, 7, and 8 of the Muzychuk-Koneru match (with notes) and games 1 and 2 of the A. Muzychuk-Lei match (without notes) are here.
I'd assumed – possibly incorrectly – that the reason for the strange format of this event is not to use it as an experiment, as you state, but rather to keep the two Ukrainian and three Russian players apart from each other for as long as possible (and perhaps altogether). The only basis for my assumption is that this is what's actually happened, but it could be a coincidence, of course.
The reason 7...Nc6 is to be avoided is 8.Nf3 Nf6 9 Qb3, while 7...Nf6 8.Qb3 can be met with Na6.
The old lines with ...O-O-O don't look good because ...g4 can be answered with Nh4. This knight blocks Black's attack, as shown in several corr. games.