At the end of a tournament where nearly 80% of the games were drawn, a record for an elite event, player power finally settled the $300,000 (£230,000) Sinquefield Cup at St Louis this week. The world champion, Magnus Carlsen, his challenger, Fabiano Caruana, and the world No 6, Levon Aronian, were declared joint winners following a dispute over the tiebreak rules.

The regulations stated that the top two from this trio, who all scored 5.5/9, would play off for the trophy. There was a snag, though. They had drawn all their mutual games, had the identical number of wins (two) and had the identical number of wins with Black (zero).

Carlsen and Aronian objected to the fourth tiebreak, a random drawing of lots, and proposed a three-way play-off. Caruana refused that option since he had to face a separate play-off on the same day for a place in the Grand Tour final in December. The trio then proposed that the Sinquefield title be shared, and the organisers, faced with an unthinkable alternative scenario of defaulting the world champion or his challenger, agreed.

It was a pragmatic decision but an inelegant conclusion to a tournament which had the strictest possible anti-draw rules yet was still dominated by half points.

Such a confusing outcome has sparked criticism of the format of the Sinquefield Cup and of the five-event Grand Tour. Nine of the invitees plus a wildcard compete in each event. Critics argue that a closed shop of elite players who can keep their high ratings by drawing with each other discourages risks, as does a tournament which acts a qualifier for a more important contest, in this case the Grand Tour semi-finals and final.

The system for player selection is also controversial. Shakhriyar Mamedyarov, currently world No 3, was only given a single wildcard place before 2018. China’s Ding Liren, currently world No 4 and one of the favourites to challenge for the title in 2020, has played only as a 2016 wild card. Originally the Tour consisted solely of classical tournaments, whereas now it is dominated by rapid and blitz.

As an indicator of who will win the world title match starting in London on 9 November, the Sinquefield Cup proved inconclusive. Caruana’s two wins were smoother than Carlsen’s two long grinds, but grinding is what Magnus does best and he also had his challenger close to defeat. Carlsen is currently quoted at 2-5, strong odds on, which reflects the significant chance that the classical games will end level after 12 games and that his superior speed play will then prove decisive.

Aronian scored in style in the final round in a game which both he and Alexander Grischuk needed to win, Slightly worse on the board but with the Russian short of time, Aronian launched the speculative sacrifice 18 Rxf7! and was rewarded when his opponent missed the defence 21…Re8! and later 25…Kg6! allowing the king to find safety at h5. After Grischuk’s final error 29…Rd8?(Re8!) Aronian’s 30 Qe7! conjured up a mating attack which Black’s paralysed army could only watch.

Levon Aronian v Alexander Grischuk

1 d4 Nf6 2 Nf3 d6 3 g3 Nbd7 4 Bg2 e5 5 c4 c6 6 Nc3 e4 7 Nh4 d5 8 O-O?! Bb4 9 cxd5 cxd5 10 f3 Bxc3 11 bxc3 O-O 12 Ba3 Re8 13 Nf5 Nb6 14 Nd6 Nc4 15 Nxc4 dxc4 16 fxe4 Nxe4 17 Qc2 Qd5 18 Rxf7! Kxf7 19 Rf1+ Bf5 20 g4 g6 21 Qc1 Kg7? 22 gxf5 gxf5 23 Bxe4 fxe4 24 Qf4 h6 25 Qc7+ Kh8? 26 Bd6 Rg8+ 27 Kf2 Rg6 28 Be5+ Kg8 29 Ke3 Rd8? 30 Qe7! b5 31 h4 a5 32 h5 Rg5 33 Rf6 Rxe5 34 Rg6+ 1-0

3582 Not Black, because the king could only have reached a2 via an illegal check from an unmoved white pawn. Not the imprisoned rook. Not Nb3-a1 or Kd1-c1,`because Black has no immediately previous legal move. Not the unmoved pawn trio. The WK must have captured on c1, and a knight is the only black piece which could have got there legally on the previous turn. So Kx(N)c1 is the answer.