PGB81

White 1 intends to sacrifice two stones and finish here in sente.

Black 2 takes the sacrifice. It is important: not because it is large but because otherwise White's stones on the fight would become very thick. But I believe that simply finishing off killing White's stones on the top was a sure win for Black.

White 3 continues with the sacrifice hoping that Black would reply. Then White will use sente to do something at the top. This hope is a part of the game. White gambles.

Black 4 takes the two stones and White's sacrifice has worked.

White 5 is an atari that gets some half eyes for the group at the top.

Black 6 connects (another option was to capture a stone) and White makes one more atari with 7. Black pulls out with 8 and White 9 sets up another half eye. Now killing White may be a problem. Black comes with 10 and White could live with the next move, but encouraged by sudden improvement of the situation she chooses not to do so.