Glamorgan won the toss and elected to field first in the match played at Northampton.
Ganguly opened the innings for Northants with Usman Afzaal (15) but the pair failed to give a good start to the hosts. Ganguly hit three fours in his short innings and faced 19 balls before being caught by RB Croft off the bowling of AG Wharf.
Northants posted 174 for six in their 20 overs courtesy a brilliant 29-ball 51 by DG Sales.
The deposed Team India, who celebrates his 33rd birthday today, then conceded 38 runs in his four overs but took the crucial wicket of Galmorgan top scorer Brandon McCullum (40) as the hosts restricted the visitors to 160 for six.
Ganguly's figures read 4-0-38-1.
Meanwhile, in another Twenty20 Cup match, Zaheer Khan scalped two wickets as Worcestershire handed a four-run loss to Warwickshire at Edbagston, who will find it hard to qualify for the quarter-final after this.
The visitors made 186 for five at Edgbaston after winning the toss with Ben Smith (69 not out) and Vikram Solanki (43) being the top scorers.
Warwickshire's reply was led by an unbeaten 75 by Jon Trott but Zaheer and Roger Sillence bowled economically and took two wickets each to prevent the hosts from reaching the target.
Elsewhere, Dinesh Mongia failed with the bat making just five but Leicestershire registered a 32-run victory over Durham to knock them out of the Twenty20 at Grace Road.
Electing to bat first, the 2004 champions made 144 for five with HD Ackerman making 60 and Jeremy Snape 38.
In reply, Durham were reduced to 23 for four and were eventually bowled out for 112.