Ellis Harrison at the double as Portsmouth put Birmingham to the sword in Carabao Cup first round

Ellis Harrison was at the double on his full debut, while Ben Close netted a sumptuous volley against the Championship visitors.

Kenny Jackett made three changes from Saturday’s League One defeat to Shrewsbury.

Andy Cannon was handed his first outing since January, replacing Gareth Evans in the No10 role.

John Marquis was absent because of his partner going into labour, which gave Harrison a start, while Ben Close came in for the suspended Ross McCrorie.

Pompey made a bright start to the clash.

On four minutes, Marcus Harness’ cross almost picked out Harrison lurking in the box, only for Geraldo Bajrami to make a crucial intervention.

There was a moment of panic for the hosts in the 16th minute when Ronan Curtis’ clearance at the near post cannoned off his own crossbar.

Jackett’s men started to take control, though, causing problems from several corners.

And it was no surprise when the opener arrived from a set-piece on the half-hour mark.

Tom Naylor’s header at the back post hit Steve Seddon, but the ball fell kindly for Harrison.

The former Ipswich man’s header was cleared onto the underside of the crossbar by Wes Harding but referee Neil Hair deemed the ball had crossed the line.

To their credit, Birmingham made a good response, with Craig Gardener forcing a decent stop from home keeper Craig MacGillivray.

But Pompey continued to press their foot on the gas – with Close netting a superb goal six minutes before the break.

Curtis’ deflected effort fell perfectly for the academy graduate and he timed his volley to perfection to find the bottom corner from 20 yards.

The Blues were rampant and almost had a third in stoppage-time when Curtis’ angled drive flashed beyond the far post.

Jackett’s men opened the second half in the same scintillating fashion and put the tie beyond reach in the 54th minute.

Curtis’ inch-perfect cross picked out Harrison at the back post and he rose well to head home and notch his second of the game.

The summer signing from Ipswich must have thought he had a hat-trick on 65 minutes but was denied by a smart save from visiting keeper David Stockdale.

The rebound fell kindly for Lee Brown, although he was unable to hit the target with the goal gaping.

Pep Clotet’s side looked to find a away into the game, with Charlie Lakin unable to keep an effort down in 71 minutes.

And with 10 minutes remaining, MacGillivray made a flying stop to his left to thwart Gardener’s stinging 30-yard free-kick.

At the death, the home keeper again made a remarkable save to prevent the Brum skipper for a third time in the clash.

But Pompey got the job done and booked their spot in the second stage of the competition for the first time since Jackett took the reins.