Nikolay Davydenko produced a ruthless display to beat U.S. Open champion Juan Martin Del Potro in straight sets to win the ATP World Tour Finals in London on Sunday. Davydenko had dispatched world number one Roger Federer in the semifinals and re-produced the magic to see off the Argentine 6-3 6-4 in one hour and 23 minutes at the O2 Arena. The victory in the elite, eight-man end-of-season showpiece is the highlight of the 28-year-old Russian's career, going one better than 2008 when he lost in the final to Novak Djokovic of Serbia. Davydenko, seeded sixth, had begun the week with a thrilling three-set loss to Djokovic in round-robin play, but proceeded to rack up four straight victories, culminating in his emphatic win over fifth-ranked Del Potro. It earned him $1.5 million and he was delighted to have captured the first major trophy of a career marked by consistency but mostly in a support role to the game's very elite. For me it was amazing coming here number seven and winning the tournament. I surprised myself, he said. Del Potro looked weary after his epic three-set semifinal win over Swede Robin Soderling the previous night. He dropped his service in the fourth ganme of the opening set and could claim only five points on his opponent's service as the Russian eased to an early lead. The second set was tighter, with Del Potro having a break point in the sixth game. But at