Aaron Thomason held his nerve to defend 13 from the final over as Birmingham beat Northamptonshire by just two runs at Wantage Road to go top of the North Group of the NatWest T20 Blast.

20-year-old Thomason, playing just his 13th T20 match, was trusted with the final two overs of the game from the Wilson End when 27 were needed from 18 balls. He conceded only 7 and then Jeetan Patel presented the youngster with 13 to defend from the final six. Alex Wakely struck the second ball of the over for six down the ground but despite reducing the equation to 4 from 2 balls, Thomason held the game for the Bears.

Ian Bell, Warwickshire's captain, said: "It was a great win to get over the line when we didn't play our best, to come to Northampton is tough. Aaron didn't shy away he wanted that last over so I'm really happy. He's someone who works hard at his slower balls and yorkers and listens to the guys who have played around the world."

It was a chase that Northamptonshire were always well in touch with - and Wakely's 52 from 34 balls appeared to be steering them home - but they could never kill the game and missed the chance to move to the top of the group themselves.

Adam Rossington and Richard Levi took 78 from their previous Powerplay and here again got their side off to a flier with 51 from the first four overs. Rossington struck boundaries from the first three balls of the second over, two of them slapped wide of midwicket.

Levi then flicked Colin de Grandhomme over square leg for the innings' first six and drove four more past cover point. But having smashed Thomason for a huge six into a mobile bar over midwicket, the bowler exacted his revenge with a decent yorker.

Patel then picked up Rossington, caught at deep midwicket for 43 from 30 balls, and Ben Duckett for 9 in successive balls to get Birmingham back into the innings. The wicket of Duckett was a beauty from round the wicket that turned and took the top of off stump.

The wicket of Duckett gave way to four cheap overs that left 64 needed from 42 balls only for Wakely to flick two fours off Boyd Rankin and cut another to ease the tension and when he skipped down the pitch to flick the first ball of Patel's third over over midwicket for another boundaries, the hosts were back in charge of the chase.

But de Grandhomme found a yorker to remove Rob Keogh for a run-a-ball 18 and Steven Crook holed out to mid-off second ball to leave 27 needed from 18 balls. Thomason and Patel then finished the game off.

Birmingham's 172 for 9 was a stop-start effort where they lost wickets regularly and four set batsman fell when set to cause greater damage.

Having been sent in, they made 40 for 1 in a Powerplay that featured some seam movement on a fresh wicket and following afternoon rain. Ed Pollock played a remarkable flick over deep square for the night's first six but, hurried by a Rory Kleinveldt back-of-a-length ball, was caught behind off a big top edge. Sam Hain slog swept Richard Gleeson for six over long leg and both he and Ian Bell, got inside edges for four to fine leg.

Bell was notably scratchy, beaten outside off several times, and fell for 16 from 18 balls trying to reverse-sweep Keogh's second ball and losing his off stump.

Adam Hose, after 76 on his county debut on Sunday, shimmed down the wicket to slap Nathan Buck for four and then struck a might six that found the roof of the Lynn Wilson centre off Keogh. But when he clipped a low full-toss from Keogh to midwicket and Sam Hain was run out after a calamitous mix up with de Grandhomme, Birmingham had lose both set men and were 82 for 4 after 11 overs.

De Grandhomme atoned for his part in the mix up by striking three fours and a six from the 14th over bowled by Sanderson that conceded 21 and an over later, Birmingham were well placed at 128 for 4 after 15 overs. But again, Northants picked up a useful wicket with de Grandhomme, after going dangerously to 37 from just 15 balls, picked out deep square. Patel struck a six in the final over to nudge his side to a score that proved enough.