Chess lecture on March 14 by Erik Malmsten
This position usually arises after a player has promoted a pawn. It is a very complicated win. The computer database found it a win in less than 35 moves with best play. Even after getting the defending King to the back rank it can still take 20 moves, although the last eight or so are Queen and King mating the bare King. I find an open board with over 20 possible Queen moves difficult, but the attacker has to look only for the interconnecting squares to fork the King and a wandering Rook. A good technique is to put the Queen on a diagonal next to the diagonal that attacks the Rook. The winning position comes when White can threaten a back rank checkmate and the rook.
The defender can also fork, skewer and has some stalemate threats. Throw off the attacker enough times, such as harassment checks, and the 50-move draw comes into effect. Or with sudden-death time control, there won’t be enough time to calculate the win. So this makes it worth defending.
If you want to deeply explore this endgame search online for the training database by Derek Grimmell and practice with your computer.
White: Kc6, Qa5
Black: Kb8, Rb7
Black to move loses. White to move, White triangulates to make the
position Black to move.