Argentine Juan Martin Del Potro will meet Nikolay Davydenko in the final of the ATP World Tennis Tour Finals after overcoming Swedish eighth seed Robin Soderling 6-7 (1-7) 6-3 7-6 (7-3) in an equally tight second semi-final.
Del Potro roared back after a sluggish opening set tiebreak where he took a solitary point after missing four break chances across the set.
The US Open champ then upped his game to level the encounter before prevailing in the deciding breaker with a 12th ace.
