$$Wc punish w's timesuji
$$ . . . O O X . . . |
$$ . . O . O X . . . |
$$ . . O X X O X X . |
$$ X . O X . O O X . |
$$ . O . X O O O X . |
$$ . . O . O X X O 1 |
$$ . . . . . . . X . |
$$ ------------------+
[go]$$Wc punish w's timesuji
$$ . . . O O X . . . |
$$ . . O . O X . . . |
$$ . . O X X O X X . |
$$ X . O X . O O X . |
$$ . O . X O O O X . |
$$ . . O . O X X O 1 |
$$ . . . . . . . X . |
$$ ------------------+[/go]
edit: hint
White, in byomi, needed sente and some time to win the game and he succeeded. Lee Changho failed to punish . should have been at Q1, a big sente move. In the game B had the chance to pay a small fee and grab sente. The tesuji is some moves later and not quite open in the air.
$$Wc
$$ . . . O O X . . . |
$$ . . O . O X . . . |
$$ . . O X X O X X . |
$$ X . O X . O O X . |
$$ . O . X O O O X . |
$$ . . O . O X X O 1 |
$$ . . . . . . 2 X . |
$$ ------------------+
[go]$$Wc
$$ . . . O O X . . . |
$$ . . O . O X . . . |
$$ . . O X X O X X . |
$$ X . O X . O O X . |
$$ . O . X O O O X . |
$$ . . O . O X X O 1 |
$$ . . . . . . 2 X . |
$$ ------------------+[/go]
Now if white tenuki, black has a nasty ko with the descent at O2 (white take first, but it's huge), and P1 is not sente for white (black can recapture)
OK, problem solved, thx HH and MW, the title goes to Triss!!
edit: In the real game Lee Changho as B didn't tenuki as in MW's diagram. So W kept sente to play the winning endgame move elsewhere.