Novak Djokovic won the World Tennis Championship for a record-equalling fourth time in his career after battling back from a set down to defeat Kevin Anderson.
The world number one - who had previously won the exhibition tournament for three successive years from 2011 to 2013 - triumphed 4-6 7-5 7-5 in a highly competitive final in Abu Dhabi on Saturday.
Having beaten Roberto Bautista Agut a year ago to be crowned champion, Anderson appeared on course to retain his crown when he claimed the first set.
The South African, ranked sixth in the world ahead of the new ATP Tour season, survived a scare on his own serve in the fourth game before breaking his rival in the ninth, allowing him to serve out for the opener.
However, Djokovic hit back to make sure he would join Rafael Nadal - who had withdrawn from his third-place play-off against Karen Khachanov after his loss to the big-serving Anderson in the semi-finals on Friday - with a quartet of titles in the event's history.
Djokovic was patient before pouncing late in the second set, claiming the pivotal break in the 12th game, but was then uncharacteristically wasteful in a tense decider, with four match-point opportunities going begging.
Eventually, though, the 31-year-old secured a hard-fought victory at the fifth attempt, resoundingly ending a compelling rally with a cross-court winner off his forehand side.
With Nadal out, Khachanov instead faced Dominic Thiem in an exhibition contest, defeating the Austrian in a super tie-breaker 10-3 after they had won a set apiece.