The Scotland international drilled a free-kick into the bottom corner to break the deadlock after 58 minutes, and 18 minutes later he coolly converted from close in to seal the points and a third straight win.
Ipswich were not without their chances, though, with Frank Fielding pulling off a stunning save to deny substitute Jason Scotland late on.
Derby made one enforced change from the side which impressively turned over Portsmouth on Saturday, with Ben Pringle replacing the suspended Dean Leacock. John Brayford moved to the heart of defence, with Paul Green switching to right-back.
Striker Scotland dropped to the bench for Ipswich, with youngster Connor Wickham coming in.
Rams midfielder Tomasz Cywka had the first testing shot of the evening as he let fly from 25 yards, but goalkeeper Marton Fulop tipped his effort over the crossbar.
Ipswich responded with a good spell of pressure, Tamas Priskin forcing Fielding into a decent stop with an audacious 30-yard drive and Wickham sending a shot wide from the edge of the area.
Priskin should have done better with a close-range header in the 21st minute, but he struggled for power and Fielding gratefully gathered.
Derby, who went into the game having won six of their last eight matches, hit back, with Shefki Kuqi scuffing a shot goalwards that Fulop pushed away.
James Bailey brought a superb stop from the Hungarian keeper in the 36th minute, connecting well with a Cywka cross 12 yards out, but Fulop palmed the ball around the post.
Commons' 30-yard strike and a six-yard header from Kuqi, both of which were comfortably dealt with by Fulop, brought an entertaining first half to a close.
Nigel Clough's side finally broke the deadlock in the 58th minute when Commons drilled a free-kick low and hard into the bottom corner after he had been brought down by Tom Eastman.
Ipswich almost equalised straight from the kick-off when the ball fell for Grant Leadbitter inside the area, but his powerful shot was parried by Fielding.
Substitute Scotland was denied by the keeper in the 70th minute, and shortly afterwards the Rams doubled their lead.
Dean Moxey burst into the area and cut the ball back for Commons to slot home from eight yards. Commons was substituted seconds later, with Stephen Pearson coming on.
Ipswich piled forward as time ticked on, and Scotland was holding his head in disbelief as Fielding somehow kept out his close-range shot with four minutes left.
Tommy Smith's header was well-held by Fielding at the death as Derby held on.