Saints tasted the bitter side of cup football as former academy product Theo Walcott bagged a hat-trick as Arsenal handed out a 5-0 thrashing to dump Saints out of the FA Cup just three days after Claude Puel’s men beat Liverpool to reach Wembley.

Puel made ten changes to the side that won at Anfield to reach the League Cup showpiece, but a weakened Arsenal side were comfortably better and handed Saints a thrashing in a one-sided game at St Mary’s.

Former Saints star Theo Walcott scored three goals in the fourth round tie against his old club, with Danny Welbeck bagging a brace.

Arsenal put Saints under pressure in the opening stages and threatened after just three minutes.

A quick counter attack saw Theo Walcott get to the right by-line and cut back to Jeff Reine-Adelaide, but his shot from just inside the area was charged down by Jack Stephens.

Arsenal were knocking on the door again moments later as Lucas Perez flashed a cross into the six yard box but nobody was able to get on the end of it.

Saints were really struggling to cope with the Gunners, were giving the ball away cheaply, and were relieved to see Alex Oxlade-Chamberlain’s shot from 20 yards whistle wide of the post.

The inevitable happened on 15 minutes as Arsenal got the goal they had been threatening since the off.

Saints had dropped so deep but were still allowing space in behind to runners, and when Ainsley Matiland-Niles’ ball was flicked round the corner by Perez, it played Welbeck in on goal.

He produced an excellent chipped finish to lob the advancing Harry Lewis, with the ball clipping the underside of the bar on its way into the net.

It got even worse as Saints contributed to their own downfall as Welbeck scored again on 22 minutes.

The goal came from a high ball forward from inside his own half by right back Hector Bellerin.

Welbeck was lurking on the shoulder of the last man, in this case Stephens, and, despite an average first touch as he brought the ball down, goalkeeper Lewis had got lost in a no man’s land in the penalty area and the Arsenal man was able to finish low through his legs.

Saints finally created something a couple of minutes later as David Ospina ended up on the ground outside his area trying to chase down Shane Long, but when the ball dropped in the area to Pierre-Emile Hojbjerg he volleyed over the bar.

Long managed to work Ospina moments later as he shot from a difficult angle after intercepting Cuco Martina’s curling ball forward, but the Gunners keeper dived to turn it away.

Arsenal should have had a third on 29 minutes when Shkodran Mustafi was able to meet a right wing free kick inside the six yard box but he flicked his header wide of the far post.

Hojbjerg tried his luck from a free kick just outside the box but could only curl his effort round the outside of the wall and into the side netting.

Saints were staring a hammering square in the face when Arsenal scored again on 35 minutes.

Once more they played a large part in their own demise with Stephens slamming a ball into Hojbjerg to hand possession to Arsenal.

They moved quickly with Perez giving Welbeck the chance to play in a cross from the left by-line.

Sam McQueen stood still in the six yard box ready to clear but Theo Walcott nipped in in front of him to have the simple task of finishing for 3-0.

Josh Sims had a chance to try and pull one back in first half stoppage time after Martina robbed Kieran Gibbs of the ball and cut it back, but a heavy first touch allowed the ball to get away from him.

Arsenal continued on the front foot at the start of the second period, and Bellerin might have done better than pick out Lewis when found in the area eight minutes after the restart.

Saints made a double change in a last bid to try and find a goal that would work them back into the game with Dusan Tadic and Nathan Redmond replacing Lloyd Isgrove and Long on 64 minutes.

Arsenal responded by bringing on Alexis Sanchez for Welbeck in attack.

Jordy Clasie tried to make something happen with a shot from 25 yards but it sailed well over the bar.

However, Arsenal put the tie beyond any doubt as they scored again on 69 minutes.

It was another fast flowing move as Alex Oxlade-Chamberlain intercepted and burst forward. He played it to Sanchez on the overlap, and the sub looked up from the right by-line and cut back to Walcott, who was in space having held his run, despite there being plenty of Saints players in the box.

He produced a first time right footed finish which curled into the far corner.

Arsenal threw on more firepower with Alex Iwobi coming on for Reine-Adelaide.

In truth, Arsenal lost some of their impetus in the closing stages knowing that they had already done more than enough to book their place in the fifth round, but that didn’t stop them from adding another goal with five minutes remaining.

It was another quick break from Arsenal with Sanchez holding the ball up and waiting for the run of Walcott to his right.

He slipped the ball into the former Saints academy product who coolly slotted a low finish past Lewis to make it 5-0.

It might have got even worse in the dying seconds had it not been for Lewis getting quickly off his line to block at the feet of Perez.

It was really an irrelevance at that stage though as Saints were left to focus on the Premier League campaign and the EFL Cup final for the remainder of the season as Arsenal marched on in convincing fashion.