The 31-year-old Hewitt, who has been troubled with foot, toe, hip and hand injuries in recent years, also beat Canada's Milos Raonic and Tomas Berdych of the Czech Republic at the eight-man invitational tournament.
The former world number one raced through the first set in 27 minutes before the Argentine regrouped in the second to give the second set scoreline some respectability.
"I felt like every match I got better and better and more confident," Hewitt said. "Especially my ball-striking, I felt it was really coming out of the middle of the racquet from the word go.
"I moved really well and I felt sharp out there which is a good sign. I hit the ball as well as I have in a long time."
Hewitt now looms as a dark horse at the Australian Open, where he has been drawn against Serbian world number nine Janko Tipsarevic.
"He's a quality player and he's improved a lot in the last two years," Hewitt said. "It's going to be a tough match but I'll be ready for it.
"It's nice to know that in the back of your mind you've done all the right preparation to just go out there and play."