The Carabao Cup finalist came out on the right side of a classic cup tie at St Andrew's, although it had to do things the hard way.

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Just 43 seconds had passed when City took the lead. Keshi Anderson kept a corner alive at the back post, and Ethan Laird's volley took a massive deflection off Callum Wilson, before finding the roof of the net.

Nick Pope made a fine save to thwart Jay Stansfield, then Newcastle levelled in bizarre circumstances in the 21st minute.

Willock turned William Osula's cross towards goal, only for Bailey Peacock-Farrell to claw it away from the goalline. Willock then smashed the rebound over, only for the linesman to signal his first effort had crossed the line.

With goalline technology not in use until the fifth round of the competition, the goal stood despite replays being unclear.

Five minutes later, Newcastle was ahead via another scrappy goal, Wilson prodding in after Osula blocked his own close-range effort with his standing leg.

But Birmingham restored parity five minutes before half-time, Tomoki Iwata rifling a wonderful strike into the top-right corner from the edge of the box.

There was less goalmouth action in a second half that occasionally threatened to boil over, until Willock struck the decisive goal eight minutes from time.

Sean Longstaff's cutback was charged down, but it deflected kindly into the path of Willock on the right side of the box, and he made no mistake with his finish.