Ruan Lufei - Hou Yifan
Women's World Chess Championship, Round 6.2 (2010)
Position after 36...Rxa4
Black is up two pawns, which would normally be an easy win, but rook endings are notoriously drawish. Here, White's slim chances of a draw are enhanced by the passive position of the Black rook (tied to the defense of the b4-pawn), the active positions of the White king and rook, and the facts that (1) if the b-pawn were removed, the game would be a draw and (2) an ending with just Black's f- and h-pawns will usually be a draw.
37.h4 Kf8 38.Re4 f6 39.Rd4 Ke7 40.Rd4 Ke6 41.Ke4 Ke7 42.Kf4
White is asserting that Black cannot make any progress. She will just shuffle her king between e4 and f4. Black can try to make progress by taking one of these squares away from the White king: if she plays h6 and g5, then f4 is off limits. Thus 42...h6 43.Ke4 Ke6 (so that ...g5 comes with check, preventing White from answering it with h5) 44.Kf4 g5+ 45.hxg5 hxg5+ 46.Ke4 Ke7, and White has to give way, either allowing the rook to shift away from a4 with check or allowing the Black king to advance to the queenside.