user13147: The other day I witnessed a National Master fail to checkmate using a queen vs rook. While it was blitz, it seemed like the national master didn't know Philidor's position.
Question: Is pawnless queen vs rook perhaps not so common in practical play? I believe Philidor's position is indeed common for practical play.

user4393: The problem is that winning with a Q v R requires multiple quiet moves which are not obvious at all to a human in blitz play. Not to mention these type of endgames are really only studied by GMs because at master level these endgames do not happen enough to justify studying them extensively. And even GMs screw up these type of endgames like RB V R or even RK v R in classic time controls fairly often.
http://www.chessgames.com/perl/chessgame?gid=1070866
Kasparov won a dead drawn endgame that even I should be able to draw no problem.

user7297: Some pawnless endgames, like mating with bishop and knight, or the queen vs. rook case you mention, just don't occur that much in practice, especially compared to pawn endgames or rook endgames. That means players are less likely to study them, and unfortunately for those players, in these endgames one often can't rely on general principles (rooks behind passed pawns or on the 7th rank, weak vs. strong bishops). I doubt masters would have any difficulties with a king + pawn vs. king endgame.
Also, let me quote Karsten Müller and Frank Lamprecht from their book Fundamental Chess Endings:

The queen always wins against a lone rook unless there is an immediate draw such as perpetual check or stalemate. The winning nature of the ending has been known for a long time and it was believed to be quite easy to force a win. However, the appearance of computer databases in 1978 caused the ending to be seen in a new light. While they confirmed that the queen should win from all normal starting positions, they also showed that it was quite difficult to win if the defender played precisely.

(emphasis mine)

13147: <p>The other day I witnessed a National Master fail to checkmate using a queen vs rook. While it was blitz, it seemed like the national master didn't know Philidor's position.</p>
<p><strong>Question</strong>: Is pawnless queen vs rook perhaps not so common in practical play? I believe Philidor's position is indeed common for practical play.</p>
 4393: <p>The problem is that winning with a Q v R requires multiple quiet moves which are not obvious at all to a human in blitz play. Not to mention these type of endgames are really only studied by GMs because at master level these endgames do not happen enough to justify studying them extensively. And even GMs screw up these type of endgames like RB V R or even RK v R in classic time controls fairly often.</p>

<p><a href="http://www.chessgames.com/perl/chessgame?gid=1070866" rel="nofollow noreferrer">http://www.chessgames.com/perl/chessgame?gid=1070866</a></p>

<p>Kasparov won a dead drawn endgame that even I should be able to draw no problem.</p>
 7297: <p>Some pawnless endgames, like mating with bishop and knight, or the queen vs. rook case you mention, just don't occur that much in practice, especially compared to pawn endgames or rook endgames. That means players are less likely to study them, and unfortunately for those players, in these endgames one often can't rely on general principles (rooks behind passed pawns or on the 7th rank, weak vs. strong bishops). I doubt masters would have any difficulties with a king + pawn vs. king endgame.</p>

<p>Also, let me quote Karsten Müller and Frank Lamprecht from their book Fundamental Chess Endings:</p>

<blockquote>
  <p>The queen always wins against a lone rook unless there is an immediate draw such as perpetual check or stalemate. The winning nature of the ending has been known for a long time and it was believed to be quite easy to force a win. However, the appearance of computer databases in 1978 caused the ending to be seen in a new light. While they confirmed that the queen should win from all normal starting positions, they also showed that it was <strong>quite difficult to win if the defender played precisely.</strong></p>
</blockquote>

<p>(emphasis mine)</p>
