Darren Bent scored the winner from the spot as Derby beat Birmingham 1-0 to move within a point of the Sky Bet Championship play-off places.
The Blues kept their hosts at arm's length for long periods but experience played a part as Richard Keogh went down under the grip of Michael Morrison and former Aston Villa frontman Bent swept home the penalty in the 64th minute, celebrating in front of the fans of his former rivals.
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It is a sixth victory in seven games for the Rams and a seventh consecutive home clean sheet - a club record - but a second straight loss for new Blues boss Gianfranco Zola.
From the first whistle, it looked like it would be a game of few opportunities, Derby recording half-chances from Johnny Russell and Bent but Birmingham creating little of note.
Derby pressed the Birmingham backline early on, coercing their opponents into minor mistakes, but were forced to rethink their plans when Martin Olsson pulled up after five minutes, clutching his hamstring.
His replacement was the returning Ikechi Anya and from the moment he was introduced, it looked clear he was to be the driving outlet on the left.
Russell was the force behind the first real chance of the first 45 minutes, though, swinging in a cross that Bent flicked just past the post.
What proved to be Birmingham's best opportunity of the game came after 25 minutes when Chris Baird sent a wayward lofted pass-back in the direction of Scott Carson, who just managed to head the ball away from the advancing Blues frontman, Lukas Jutkiewicz.
Russell was again involved just after the half hour when his cross was pushed away by Tomasz Kuszczak, but for all the Derby pressure, Birmingham always looked like they might hit them on the counter.
At the break, the two sides were level but Kuszczak was again the hero nine minutes into the second half; Bent tracked Shotton's headed pass-back, reached it before the stopper and flicked towards goal. The Pole rushed out with flailing arms and heroically blocked the shot.
Only minutes after the hour mark, however, his heroics were forgotten when Derby took the lead from the spot.
Defending a corner Morrison tussled with Keogh, who gestured to the referee and Bent duly stepped up to stroke home his fourth of the season.
Substitute Diego Fabbrini was bullied off the ball by Baird as he tried to convert Che Adams' blocked shot but that was as good as it got.
Birmingham's play-off push is slowing down after two straight defeats under Zola, while Derby earned a priceless three points in their search for a top-six place.