Until Alexander Hleb opened the scoring at Bloomfield Road, Blackpool had been able to exploit a compact Birmingham City defense by building attacks down the flanks with relatively little resistance. Roger Johnson's strong play in the middle helped Brum thwart each Tangerine entry, but Blackpool was able to dictate tempo and, with the exception of two counter attack chances for Brum, all of the goal scoring opportunities.
While Brum's scoring chances have stayed infrequent in the wake of the goal, they've been able to make an adjustment that's help them provide more resistance down the flanks. At least, it seems like an adjustment - this could be improved effort or what they have wanted to do all along. Regardless, Blackpool is finding their life harder in the last 20 minutes of the first half.
That apparent adjustment finds Barry Ferguson and Keith Fahey, the wide players in Alex McLeish's line of four in midfield, jumping out to challenge on the flanks. By is a fullback in possession or one of Blackpool's wide players trying to come forward, Brum is now sending a man after them, occupying the vacated space with one of the midfielders while Matt Derbyshire, drops from his forward position.
While Derbyshire isn't dropping all the way back into the final third when Blackpol's able to get into attack, he is dropping deep enough to maintain numbers in midfield when Ferguson and Fahey are challenging in the middle third. Effectively, this may have changed McLeish's shape from what looked like a two striker formation (Derbyshire along with Cameron Jerome) to a 4-4-1-1 - closer to Brum's base formation.
The result: Blackpool has had to be more patient moving the ball into attack, and once there, they're finding a Birmingham defense whose shape has not had to be compromised. As a result, the match goes to half 1-0 Brum, but Birmingham having gained a firm grip on play.