Del Potro hammered six aces and saved the only two break points he faced to win his fifth match since returning in February at Delray Beach.
Del Potro struck the ball solidly on serve and from the forehand side and mixed in mostly slice along with a sampling of two-handed backhands to keep Pella at bay. After getting blown off the court in the first, Pella had his chances in the second set.
The 25-year-old had the only break point of the stanza and was on serve late in the tiebreaker, but made back-to-back errors to give Del Potro the victory in 88 minutes. The 27-year-old has now won seven straight against his compatriots dating back to a 2008 loss to David Nalbandian. Del Potro owns a 5-15 lifetime record against Federer (5-10 on hard courts).
Federer, returning from knee surgery in late January, has not played a match since his loss to Novak Djokovic in the semifinals at Melbourne.