The frontman set the Magpies on their way with a quick-fire brace midway through the first-half, rising high to head home Mohamed Diame’s cross 18 minutes in before netting his second with a poacher’s finish.
Birmingham – a lofty fifth ahead of the clash – failed to force Karl Darlow into a save of any sort during a one-sided opening period, and early into the second, they found themselves further behind.
Yoan Gouffran was the scorer, drilling home from a tight angle after a well-worked set-piece.
Gayle then notched his third with his last action of the afternoon, securing the match ball with another confident finish from a central position.
Setting the tone for what was to follow, United were first to go close ten minutes in. Though he had room to shoot himself, Gouffran opted to pick out Gayle with a cutback, and the frontman’s low-struck effort was pushed wide by experienced ‘keeper Tomasz Kuszczak.
From the resultant corner, Ciaran Clark’s thumping header was parried by the Pole, before the Blues cleared their lines.
Newcastle continued to make all of the running early on, and – on the quarter-of-an-hour mark – Isaac Hayden curled narrowly over the top from 20 yards.
But, just moments later, the Magpies made the breakthrough. After getting the better of the Blues’ Ryan Shotton, Diame swung in a superb cross from the right, and Gayle’s downward header proved too powerful for Kuszczak.
He did not have long to wait for his second. With 24 minutes on the clock, Hayden did brilliantly to charge between two visiting defenders, and the midfielder’s driven cross took a touch off Robert Tesche before falling kindly for Gayle, who made no mistake from close range.
Within the blink of an eye, Jonjo Shelvey almost extended Newcastle’s advantage, forcing Kuszczak into a two-handed stop from 25 yards.
Another Diame ball from wide then bounced up for Gouffran on the edge of the penalty area, who curled wide with a right-footed effort.
Birmingham began to shore up as the interval drew closer, though Shelvey did call Kuszczak into action once more before the half was out.
Shelvey – who saw the red card he picked up against Nottingham Forest rescinded earlier this week – had a key part to play in United’s third.
After Matt Ritchie’s set-piece was played short, Shelvey picked out Gayle’s run with a lofted pass, and the frontman helped the ball on for Gouffran six yards out, who duly lashed home.
Only a superb save from Kuszczak denied Gayle his third after 65 minutes. The ex-Crystal Palace forward took aim after latching onto Diame’s clever pass through the middle, only to see his left-footed strike tipped wide by the stopper.
Five minutes later, the Blues finally tested Darlow for the first time
Substitute Lukas Jutkiewicz connected with Josh Dacres-Cogley’s inviting ball from the right, but his powerful header was parried by the Magpies’ ‘keeper.
Debutant Corey O’Keeffe then scuffed wide with just Darlow to beat, but – in truth – the visitors looked long dead and buried.
And, two minutes later, they were undone for a fourth time, as Gayle converted Shelvey’s cutback after the midfielder’s burst to the byline.
Christian Atsu – a replacement for Gouffran – almost added a fifth late on, only to see a vicious left-footed attempt fly narrowly wide of Kuszczak’s near post.
Newcastle United: Karl Darlow, Vurnon Anita, Ciaran Clark, Jamaal Lascelles, Paul Dummett, Jonjo Shelvey, Isaac Hayden (Achraf Lazaar 81), Matt Ritchie, Mohamed Diame, Yoan Gouffran (Christian Atsu 71), Dwight Gayle (Aleksandar Mitrovic 78).
Substitutes not used: Matz Sels, DeAndre Yedlin, Chancel Mbemba, Cheick Tiote.
Birmingham City: Tomasz Kuszczak, Ryan Shotton, Josh Dacres-Cogley, Michael Morrison, Jonathan Grounds, Robert Tesche (Maikel Kieftenbeld 46), Stephen Gleeson, David Cotterill (Corey O’Keeffe 74), Greg Stewart (Lukas Jutkiewicz 46), Che Adams, Clayton Donaldson.
Substitutes not used: Adam Legzdins, Paul Robinson, Viv Solomon-Otabor, Reece Brown.
Bookings: Newcastle United – Matt Ritchie (59), Isaac Hayden (75); Birmingham City – none.
