user11694: Typical arguments for the longest possible game of chess take a form something like this.
1) Each player moves their knights back of forth 49 times
2) Each player moves one pawn forward one square and repeats the knight shuffling.
3) Once all pawns are on the 4th and 5th ranks, ....
and so on. 
I,we found estimates around 9000. I'm interested in the longest possible game of chess, with the restriction that the players are actually trying to win, and not cooperating to make the longest possible game allowable by the rules. We might call this the longest realistic game of chess.
Since the above argument totally breaks down, what are some new considerations that might allow us to lower the upper bound on the longest realistic game of chess?

user10380: If, in some chess position, one side can win against any defence, then we may ask what the least n, where the winning side can guarantee to checkmate in n moves or fewer, against any defence.
Analysis of seven-piece positions has brought to light some positions where n is as large as 549, for example this one in KQPKRBN.
Presumably if the number of units allowed on the board were increased, there'd be positions whose shortest wins are even longer.
But for a game to reach such a position, one side must have already blundered a half-point (supposing that the initial position is a draw with best play). So long as neither player blunders into a position where the other player can force a win, how do you decide which possible moves are co-operative and which are not?

user18809: The longest game I've ever found in tournament play is Nikolic - Arsovic, played in Belgrade in 1989. You can watch it here. It ended in a draw after 269 moves in a rook+bishop-vs-rook endgame

11694: <p>Typical arguments for the longest possible game of chess take a form something like this.</p>

<p>1) Each player moves their knights back of forth 49 times
2) Each player moves one pawn forward one square and repeats the knight shuffling.
3) Once all pawns are on the 4th and 5th ranks, ....
and so on. </p>

<p>I,we found estimates around 9000. I'm interested in the longest possible game of chess, with the restriction that the players are actually trying to win, and not cooperating to make the longest possible game allowable by the rules. We might call this the longest realistic game of chess.</p>

<p>Since the above argument totally breaks down, what are some new considerations that might allow us to lower the upper bound on the longest realistic game of chess?</p>
 10380: <p>If, in some chess position, one side can win against any defence, then we may ask what the least n, where the winning side can guarantee to checkmate in n moves or fewer, against any defence.</p>

<p>Analysis of seven-piece positions has brought to light some positions where n is as large as 549, for example <a href="http://tb7.chessok.com/articles/Top8DTM_eng" rel="nofollow noreferrer">this one in KQPKRBN</a>.</p>

<p>Presumably if the number of units allowed on the board were increased, there'd be positions whose shortest wins are even longer.</p>

<p>But for a game to reach such a position, one side must have already blundered a half-point (supposing that the initial position is a draw with best play). So long as neither player blunders into a position where the other player can force a win, how do you decide which possible moves are co-operative and which are not?</p>
 18809: <p>The longest game I've ever found in tournament play is Nikolic - Arsovic, played in Belgrade in 1989. You can watch it <a href="https://www.chessgames.com/perl/chessgame?gid=1268705" rel="nofollow noreferrer">here</a>. It ended in a draw after 269 moves in a rook+bishop-vs-rook endgame</p>
