The Argentine has recently returned after wrist surgery and proved his fitness by battling back from a set down to claim a 4-6 6-2 6-2 victory over the world No 18 from Italy.
Following his 10-month injury absence, organisers handed Del Potro a wild card for the event and there were concerns about his fitness when he received treatment on his problematic wrist in the first set.
But the former world No 4 showed glimpses of his best form as the match progressed and was pleased with his serving and ground strokes after staying on course for another final appearance.
“I thought I played better. I feel better on the court, especially in the end of the match,” said Del Potro.
“I serve well, I hit good forehands, and my backhands improved from yesterday to this match a little bit.
“I need to keep playing with these guys, hitting the ball as fast I can and keep trying.
“My wrist is the same. It’s not getting worse, so I have confidence with that. Of course I’m very happy to beat my first top 20 player of the year.”
Asked about the treatment he received, the 26-year-old said: “I’m feeling okay. It was nothing dangerous, because I sweat too much and the tape goes out, but nothing special.
“It’s like spray to keep the tape on.”
Del Potro is warming up for the upcoming Australian Open, where he has reached the 2009 and 2012, and will next face Kazakhstan qualifier Mikhail Kukushkin, who upset sixth-seed Pablo Cuevas 7-5, 7-5.
Second-seed David Goffin also crashed out after suffering a 6-3 6-3 defeat to Simone Bolelli.??