Brett Pitman netted a 32nd minute equaliser from the penalty spot as Town and Birmingham drew 1-1 at Portman Road, David Cotterill having put the visitors in front 10 minutes earlier.
Winger Larsen Touré was handed his full league debut with Ryan Fraser, dropping to the bench having ben a doubt after taking a kick in Tuesday’s 1-0 win at Leeds.
Up front, McCarthy started with Pitman and Freddie Sears with Daryl Murphy and David McGoldrick on the bench.
Birmingham made three changes, Andrew Shinnie, Neal Eardley and Demarai Gray coming in for Jon Toral, Paul Caddis and Jacques Maghoma.
The Blues started on the front foot and in the third minute Pitman hit a low 25-yard shot which Birmingham keeper Tomasz Kuszczak claimed down to his right.
On six Touré won a corner on the right, Ainsley Maitland-Niles sending over the flag-kick and a defender diverting it over ahead of Tommy Smith.
A minute later, Maitland-Niles cut the ball back from the left of the area to Sears, who shot only just over Kuszczak’s goal.
The Blues continued to press, Pitman heading a looping 10th minute right-wing Touré cross wide.
David Cotterill picked up the game’s first yellow card for a late challenge on Touré with Town on the break after the former Bristol City man had lost possession to Maitland-Niles on halfway.
Birmingham threatened for the first time in the 13th minute but Town skipper Luke Chambers blocked Shinnie’s powerful shot on the edge of the box.
Moments later, left-back Jonathan Grounds exchanged passes with Shinnie and broke into the area on the left but Dean Gerken was off his line quickly to block. Play continued and Cotterill chipped weakly into Gerken’s arms.
The Birmingham winger hit a subsequent shot well wide on 16, then two minutes later Touré was even more wayward at the other end, his strike flying deep into the lower tier of the Sir Alf Ramsey Stand.
Town had begun the game strongly but the visitors had started to look the more dangerous side and in the 22nd minute they went in front, although with some element of good fortune.
Shinnie latched onto a flick-on from a throw on the left and, as Christophe Berra lost his footing on the wet pitch, broke into the box before finding Cotterill breaking into the area on the right, and the Wales international smashed the ball past Gerken.
However, the lead would last only 10 minutes with the Blues getting back on terms in the 32nd minute from the penalty spot.
Maitland-Niles made a superb run from inside his half and just about reached the ball on the byline and cut it across but into Kuszczak’s arms. As he crossed Jonathan Spector dived in and, after the ball had gone, took the on-loan Arsenal man’s legs from under him.
Despite there being few appeals from Town players, referee Keith Stroud pointed straight to the spot, much the anger of the Birmingham players who protested bitterly. Pitman took the spot-kick and confidently beat Kuszczak to net his third goal of the season.
Cotterill forced Gerken into an uncomfortable save in the 34th minute after a freekick had been harshly awarded against Jonathan Douglas on the left, five yards outside the area. The Birmingham winger’s shot moved wickedly in the air and Gerken only just pawed it away from goal.
Town claimed another penalty a minute later when Sears went to ground under pressure from Eardley but the Town striker appeared to have been fairly outmuscled and the initial challenge looked to be outside the area in any case.
Cotterill continued to try his luck from distance, shooting wide in the 41st minute, prior to Maitland-Niles twisting and turning five yards outside the Birmingham box and hitting a shot well over.
As the half moved into injury time Paul Caddis replaced the injured Eardley for the visitors.
Neither side threatened again before the whistle ended an entertaining and open half with the scoreline a fair reflection of the game.
The Blues started well but failed to make their early dominance tell. The visitors began to get more into it and Grounds had had the game’s best chance prior to Cotterill’s goal, which owed much to Berra’s slip.
Town hadn’t looked particularly like getting on terms until the penalty, which was the result of a tremendous Maitland-Niles run.
While Spector certainly arrived late and caught the Blues winger, it was the type of foul which is usually given outside the area but less often in the box. Pitman took his penalty with great composure to leave the scores level at the break.
Birmingham youngster Gray scraped the first shot of the second half well wide two minutes after the restart.
The Blues weren’t far away from going in front in the 52nd minute when Maitland-Niles and Pitman both showed clever feet in the area before eventually finding Sears to the right of the box.
The ex-Colchester man hit a low effort back across Kuszczak but sub Caddis cleared off the line. Following the corner, Touré shot over. On 59 Douglas was booked for a foul on Shinnie.
Three minutes later, after a lengthy bout of head tennis, Touré crossed from the right and Pitman just about got his head on the ball under pressure and it bounced wide.
Tommy Smith made a vital block from Clayton Donaldson in the 64th minute after initially appearing to misjudge the flight of Michael Morrison’s cross from the right and allowing the Birmingham frontman to get in a shot. Two minutes later, Murphy replaced Pitman for the Blues.
A ball over the top sent Gray in on goal in the 68th minute but it appeared to get caught under his feet and a combination of Chambers, Smith and Berra crowded him out.
Town went close a minute later when Maitland-Niles’s corner from the left reached Chambers but too quickly for the Town captain to react. He stuck out an instinctive foot and the ball flew wide, just beyond Murphy.
The Blues continued to look the more dangerous side, Spector doing well to get the ball away from Murphy from Chambers’s cross. On 71 McGoldrick took over from Touré, who was warmly applauded off the field.
A minute later, Town had a great opportunity to claim the lead for the first time. Knudsen’s cross from the left fell to Maitland-Niles eight yards out but the 18-year-old screwed his shot well wide much to his frustration.
Gerken was out quickly to clear ahead of Donaldson in the 76th minute. Soon after, Donaldson went to ground under pressure from Smith and claimed a rather ambitious penalty. On 80 Maitland-Niles was given a warm ovation when replaced by Fraser.
Two minutes later, McGoldrick whipped over a low cross from the left which Grounds turned behind ahead of Murphy.
And from the resultant corner, the Irishman ought to have netted his first goal of the season but headed Fraser’s corner over the bar.
On 86 Berra was booked for a foul on Donaldson just outside the area to the right. From the freekick Stephen Gleeson shot wide after Cotterill had played the ball across to him.
But Town were continuing to present the greater attacking threat in the closing minutes, McGoldrick hitting a low effort across the face of goal from the right and then Skuse seeing a 20-yard shot deflect wide as the game entered its final scheduled minute.
The Blues continued to push during five minutes of injury time, Fraser hitting a low shot to Kuszczak, then Knudsen sent over a cross from the left which was missed by everyone.
Town kept up the pressure right to the whistle which came as Fraser prepared to take a corner.
A draw was probably a not unfair result but the Blues will feel they had more than enough chances to win it in the second half.
Maitland-Niles in particular will believe he should have taken his opportunity, while Murphy probably should have netted his header and Chambers might have done better with his chance, although it came very quickly to him.
The result moves the Blues up to fourth ahead of the rest of the weekend matches with Town next in action at Manchester United on Wednesday.
Town: Gerken, Chambers (c), Smith, Berra, Knudsen, Skuse, Douglas, Touré (McGoldrick 81), Maitland-Niles (Fraser 80), Pitman (Murphy 66), Sears. Unused: Bialkowski, Malarczyk, Parr, Coke.
Birmingham: Kuszczak, Eardley (Caddis 45), Spector, Morrison (c), Grounds, Gleeson, Kieftenbeld, Cotterill, Shinnie (Maghoma 73), Gray (Robinson 86), Donaldson. Unused: Legzdins, Toral, Davis, Brock-Madsen. Referee: Keith Stroud (Hampshire). Att: 18,973 (Birmingham: 471).