The visitors were ahead inside just three minutes through the highly-rated Demarai Gray but Town responded well and deservedly levelled on the stroke of half-time thanks to a superb solo effort from Nicky Adams.
Adams was impressive throughout and he put Town in front on the hour-mark with an improvised finish before Birmingham hit back through Lee Novak’s late goal to take a share of the spoils.
It was another excellent performance from the Cobblers to back up the one against Derby and they were well worth the draw after more than matching a side from two divisions higher.
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Manager Chris Wilder made five changes from the defeat to Derby with trialists Rod McDonald, Paul Corry and Sam Hoskins all starting alongside Ivan Toney, but Jason Taylor, Ricky Holmes and Evan Horwood again missed out with injury.
Birmingham brought half of their man squad, with the other half taking part in another pre-season friendly at Shrewsbury, and they named a youthful bench, although 19-year-old starlet Gray started.
The visitors needed less than three minutes to make their mark as a well-worked move resulted in the opening goal. It was created by Andrew Shinnie, whose excellent back-heel was latched onto by Lee Novak and he squad for Gray to slot into an empty net.
Town responded well to the setback and, like Saturday, saw plenty of the ball in the opening quarter and they were close to a leveller when Hoskins got away down the left and hooked the ball into the penalty area, where Toney looped a header just over.
Moments later it was Birmingham’s turn to go close when Peniel Mlapa’s sliding effort from Novak’s teasing cross dribbled wide of Ryan Clarke’s right hand post, and the German youth international went even closer minutes later as he out-sprinted the Northampton defence and placed a delicate chip over Clarke but the ball clipped the top of the crossbar.
Mlapa was proving a handful for Cresswell and McDonald and once again he almost got away but the finishing touch eluded him once more.
Cobblers gradually settled into the game and they began to have their own moments of danger with Toney slamming a free-kick into the wall before McDonald almost got a head to Adams’ devilish free-kick.
Adams was again looking sharp following his impressive display against Derby and he came closest to levelling for Northampton when he cut inside and unleashed a curling effort that dipped towards goal, but Legzdins was equal to it and tipped over.
The visiting keeper denied the same man seconds later, this time saving comfortably at his near post as the Cobblers posed more of a threat as half-time approached.
And it came as no surprise when the home side pulled level, and it was equally no surprise that the goal came from a superb bit of individual play from Adams, who cut inside and curled a fabulous low effort into the bottom corner and beyond the despairing dive of Legzdins.
That goal came on the stroke of half-time to send the teams in level at the break, and the Cobblers picked up from where they left off in the early stages of the second half with D’Ath unable to connect with Adams’ cross before Corry’s long-range effort was blocked.
Town continued to have the better of proceedings and they were deservedly rewarded on the hour-mark when Adams notched his second of the night from a brilliantly-worked move.
The winger was also the instigator when he picked out Josh Lelan and the young right-back beat his man to the touch line before pulling back for Adams to dink a cross-shot into the far corner via the woodwork.
It could have been 3-1 just moments later when good work from Alfie Potter pressurised the Birmingham defence and the ball fell to Toney inside the penalty area but he snatched at his shot and the ball skewed well wide.
Just as it seemed Town had taken control, the Blues pulled level against the run of play when Novak finished clinically from Mitch Hancox’s whipped cross.
Birmingham then looked the more likely to nick it in the final 15 minutes as Gray had an effort crucially blocked by Lelan before Clarke saved superbly from a Denny Johnstone header.
Clarke was called into an action again as he parried Novak’s powerful shot wide and that was the last attack of note as the game finished in a fair draw.
Cobblers: Clarke, Lelan, McDonald, Cresswell (Diamond 72), Buchanan, O’Toole, D’Ath (Hackett 72), Corry (Clifton 88), Toney (Richards 72), Adams (Byrom 79), Hoskins (Potter 61)
Subs not used: Warburton, Smith
Birmingham: Legzdins, Cogley, Morrison, Robinson, Hancox, Davis (Truslove 45), Gray, Griffiths (Crooks 57), Mlapa (Solomon-Otabor 77), Shinnie (Johnstone 69), Novak
Subs not used: Towsend, Cotton, McDonald
Referee: Dean Whitestone
Birmingham fans: 514