What is the best strategy for an amateur to last as many moves as possible against a GM? As an amateur chess player, I have been pondering this question for quite a bit now:


  In case of an amateur playing against a Grandmaster, what strategy would lengthen inevitable defeat?


I am assuming that a Grandmaster will always beat an amateur; I suppose that it is possible to find exceptions, but they will be so rare as to be negligible. My question is partly constrained by the following observations: 


The amateur will have a significantly higher chance of not choosing the best possible move in any given situation.
The Grandmaster is playing as if they were playing against a Master or another Grandmaster.


In this case, will the amateur be able to lengthen their defeat by always playing what they believe is the best possible move (which the Grandmaster is likely to anticipate with experience), or by using strategies that are not encouraged but objectively make the game more difficult for the Grandmaster (eg. always going for the kill regardless of piece value, a queen for a queen)?

Or would it benefit the amateur to play an entirely random move every turn, since it would prevent the amateur from taking the bait/accepting the gambit?
It really depends on what you mean by "lengthen".

I am not a GM, but as an "ordinary" Master, I have played 1700s before, who were lost by move 10, but the game still took 50 moves to finish. If you are trying to stay equal longer, that is a harder question to address.

If you are just taking about purely lengthening the game, then you are looking to trade material. Endgames naturally take longer to play out. Again, they may still be lost for many moves, but they can take 40-50 more moves to execute the opponent.

In reality, if you want a shot at being one of those statistical upsets, you want a complicated position, possibly at the cost of a pawn, where you are the aggressor. You are still likely to lose, but at least you have a "puncher's chance".

P.S. I do not recommend playing randomly. That is a recipe for making MUCH WORSE moves, which will be punished that much more severely. Unless it is an actual good move that is buried deeply, and that a strong player overlooked, a "random move" is really just a move that we discounted already, usually for good reasons. Playing moves that strong players do not consider strong, is not a good recipe for success. When I encounter such a random move, it is usually just bad, and I try to adjust to take advantage of whatever new weakness was created.

P.P.S. Based on your comment, and clarification, in the comment below, there is probably nothing you can do that will guarantee that you will stay equal longer other than if you have prepared the game with a chess database, and guess the line that the GM ultimately will play. A GM is going to be MUCH stronger positionally, and tactically. They simply analyze and understand much better.

That leads me back to my last comment above, and that is you want a complicated position. They will probably outplay you there too, but that is the only way you have a prayer.