Fourth seed Juan Martin del Potro put himself in contention for the ATP World Tour Finals when he successfully defended his Stockholm Open title on Sunday, defeating top seed and 2013 champion Grigor Dimitrov 6-4, 6-2.The Argentine, who secured his first title since he lifted the trophy in Sweden last year, dominated the final with his serve, notching up nine aces and saving all four break points he faced.Fittingly enough, Del Potro ended the championship with a big serve in the deuce court down the middle, eliciting an error from his opponent. When the ball landed in the net, Del Potro’s arms rose in celebration.”I played the best match of the week against Grigor today. Unlucky for that, sorry Grigor,” Del Potro said. “It’s amazing to come back and hold this big trophy and hopefully I can come next year as well.”Not only did Del Potro capture his 20th ATP World Tour title but he launched himself into contention for the season-ending finals in London next month. The 29-year-old will move up to 14th in the ATP’s Race to London with 2,135 points, 470 behind Pablo Carreno Busta who currently occupies the final qualifying spot.