Novak Djokovic saw off Rafael Nadal with clinical precision to reach the final and stay on track for a fourth straight ATP World Tour Finals title.
Serbia's world number one eased to a 6-3 6-3 victory, which brings him level at 23-23 in career meetings with the Spaniard.
Djokovic, 28, has now won eight of his last nine matches against Nadal.
Roger Federer plays Stan Wawrinka in an all-Swiss second second semi-final at 20:00 GMT.
More to follow