The Argentine top seed's hopes of making the eight-man season finale in London appeared to be in jeopardy when a wrist injury left him sidelined for a month but he made sure he remained in the running by winning his comeback tournament.
Del Potro won his third title of the year following his triumphs in Marseille and Estoril.
"It's important to have a good end of the year. I'm looking forward to keep improving, keep playing well at the same level as I had here," the former U.S. Open champion told reporters.
"I also look forward to London. I'm looking better to qualify there."
Del Potro currently stands seventh in the race for the Tour Finals starting on Nov. 5. Roger Federer, Novak Djokovic, Andy Murray, Rafa Nadal and David Ferrer have already booked their places.