Warwicks won the toss and opted to put Northamptonshire into bat. The game had been deemed Ladies Day to entice more females into Edgbaston and they watched on as David Sales who will not be joining Warwicks after signing a four year deal at Northants top scored with 42.
This was helped by 29 from O'Brien and 26 from Crook in a total of 137-8. Ian Salisbury did the best with the ball taking 3-14.
Jon Trott made 26 before he was run out as Warwicks struggled to get near the total. With their main batsman out, Coventrian Luke Parker and Tim Gronevald both made eighteen but Warwicks finished thirteen runs short of the required total and lost their first Twenty/20 game of the season.
Warwicks have drawn Ken Spitfires in the Quarter-Final and take on Gloucestershire in a County Championship game at Edgbaston on Sunday.