Theo Walcott and Danny Welbeck star as second-string Arsenal smash past Southampton

Southampton 0 Arsenal 5: A first-half brace from Welbeck on his first start since returning from a long injury absence set the tone for a comfortable night's work on the south coast

Theo Walcott scored his fifth Arsenal hat-trick at the club which developed his prodigious talents (Getty)

Danny Welbeck scored twice on his overdue first start of the season and former Saint Theo Walcott hit a hat-trick as Arsenal took a measure of revenge for a 4-0 Premier League thrashing by Southampton on this ground last season in a match between two much-changed teams.

But although both managers showed that the FA Cup is not their first priority, Arsene Wenger will be delighted with Welbeck's brace on his first appearance in a starting eleven since surgery on a knee injury sustained in a 2-2 draw away to Manchester City last May.

And he must also have been pleased with the display in the sometimes problematic holding midfield role of 19-year-old Ainsley Maitland-Niles, who helped create the opener and also snuffed out attacks as the home side vainly tried to get back into the game in the second half.

Ainsley Maitland-Niles put in an impressive display at the heart of Arsenal's midfield (Getty)

Both managers made ten changes to the teams that started their previous matches. Southampton at least had the excuse of a draining midweek EFL Cup semi-final cup tie at Liverpool for their reshuffle. Harry Lewis, whose only previous first-team games for the club had been in the two third-round matches against Norwich City, was in goal again.

But it was soon obvious that Arsenal's shadow side had far too much quality for their Southampton counterparts. Wenger, serving the first match of his touchline ban for pushing fourth official Anthony Taylor during the 2-1 victory over Burnley, watched the match from the directors' box armed with a walkie-talkie for communicating with the bench but had little need give many orders to Steve Bould.

Welbeck finished with aplomb to score on his first start since returning from injury (Getty)

Jeff Reine-Adelaide had a shot blocked then Lucas Perez, found on the left by Welbeck, shot past the far post. Oxlade-Chamberlain drove wide from 22 yards when unchallenged. Arsenal were largely untroubled by anything resembling a threat from Southampton and it was no surprise when they took the lead in the 15th minute with a move of real quality.

Holding midfield player Maitland-Niles, 19, making only his fourth first-team start for Arsenal, played the ball forward to Perez, whose flick sent Welbeck clear of the defence to lift the ball over Lewis and in off the crossbar.

It was his first goal since the winner in a 1-0 victory over Norwich on April 30 last year and six minutes later he had his second. Oxlade-Chamberlain's long forward pass found him accelerating away from Jack Stephens, taking the dropping ball down with his right foot and rolling it past Lewis with his right.

Walcott drove home for Arsenal's third ten minutes before half-time (Getty)

Pierre-Emile Hojbjerg volleyed over the bar as Saints looked for a reply and in the 26th minute David Ospina had to leap to palm away a shot from Shane Long after the Ireland forward had run beyond Arsenal defender Rob Holding.

But Arsenal looked capable of scoring with every attack and Shkodran Mustafi should have made it 3-0 only to glance a header just wide from a free kick on the right.

However, they did not have to wait long for a third goal. In the 35th minute Saints gave the ball away in farcical fashion as Stephens' attempted forward pass hit Hojbjerg and dropped to Welbeck. An exchange of passes with Perez took him clear of defenders again on the left and this time he cut the ball back into the middle, where Walcott got across Sam McQueen to score.

Arsene Wenger watched from the stands after being handed a four-game touchline ban on Friday (Getty)

The second half brought little respite for the home side. Hector Bellerin got forward to test Lewis with a firmly-hit shot, and Walcott lost his balance as he rounded the final defender after a promising dribble. Claude Puel put on Dusan Tadic and Nathan Redmond in an attempt to salvage some respectability but instead it was Arsenal's substitute, Alexis Sanchez, who had the greater impact.

In the 67th minute he delayed his run down the right to stay onside as he collected Oxlade-Chamberlain's pass, ran along the byline and found Walcott, who swept a low shot into the far corner. And Walcott made it 5-0, sidefooting home calmly after Sanchez had broken away down the left.

Wenger was delighted with Welbeck's contribution, and admitted that his goal-scoring return came as a slight surprise.

"I didn't expect him to be at that level," he said. "I knew that he had worked very hard but you never know how much efficiency there could be to transfer that into a competitive game. So it was great to see that he hasn't lost his runs or his finishing and shows as well that when you are was able to channel that frustration at not playing into efficiency, that's a special guy."

Southampton (4-3-3): Lewis; Martina, Stephens, Gardos, McQueen; Hojbjerg, Clasie, Reed; Sims, Long (Redmond 65), Isgrove (Tadic 64).

Subs not used: Taylor, Yoshida, Davis, Romeu, Bertrand.

Arsenal (4-1-4-1): Ospina; Bellerin, Holding, Mustafi, Gibbs; Maitland-Niles; Walcott, Oxlade-Chamberlain, Reine-Adelaide (Iwobi 72), Welbeck (Sanchez 65); Perez.

Subs not used: Martinez, Mertesacker, Gabriel, Monreal, Jenkinson.

Referee: K Friend

Attendance: 31,288