Danny Welbeck has admitted the carrot of scoring goals kept him sane during his 20 months battling two consecutive knee problems.

Arsenal's England forward fired a brace for his first goals since April as the Gunners thumped sorry Southampton 5-0 at St Mary's on Saturday.

Arsene Wenger's men cruised into the FA Cup's fifth round, with Theo Walcott also stealing a hat-trick on the south coast.

Welbeck claimed his first goals on his fourth appearance since a second bout of knee surgery inside two years, then admitted he had to keep dreaming of that moment during painstaking rehabilitation.

Asked if the hunger for goals kept him focused in recovery, Welbeck replied: "Yeah, definitely. I think because I had this experience before, coming back from an injury, I kind of knew what to expect even though it's a tough time.

"It was obviously good to be back out on the pitch after such a long time out, it's been a tough few months."

Arsenal boss Arsene Wenger was left purring over Welbeck's showing, with the 26-year-old chipping home smartly for the opener before sliding in a neat second.

Wenger admitted he had not expected Welbeck to be so sharp so soon, leaving the Gunners boss to consider the former Manchester United man ready for sterner challenges ahead.

"The end game is to be back out on the pitch and playing in the first team and I got that opportunity," Welbeck told Arsenal's official club website.

"I'm certainly looking forward to doing it many more times."

Alex Oxlade-Chamberlain tucked into a central midfield role with youngsters Jeff Reine-Adelaide and Ainsley Maitland-Niles for company.

England star Oxlade-Chamberlain laid on Welbeck's second goal with a fine raking pass, then later paid tribute to his two young midfield colleagues.

Maitland-Niles especially impressed at the base of Arsenal's midfield, the 19-year-old a constant outlet for team-mates.

"Obviously the midfielders were shuffled up a lot and we had a big responsibility," Oxlade-Chamberlain told Arsenal's official club website.

Southampton 0 Arsenal 5 player ratings Show all 22 1 /22 Southampton 0 Arsenal 5 player ratings Southampton 0 Arsenal 5 player ratings Harry Lewis - 5 out of 10 Spent most of the night picking the ball out of the net. A tricky night for the young keeper. Southampton 0 Arsenal 5 player ratings Cuco Martina - 6 out of 10 Looked lively going forward in particular playing one delicious ball forward for Long. Southampton 0 Arsenal 5 player ratings Florian Gardos - 6 out of 10 Played after a long time out but was given a difficult game. Southampton 0 Arsenal 5 player ratings Jack Stephens - 5 out of 10 Outclassed by Arsenal’s attack. Southampton 0 Arsenal 5 player ratings Sam McQueen - 5 out of 10 Not the best showing for the Saints defender. Southampton 0 Arsenal 5 player ratings Pierre-Emile Hojbjerg - 6 out of 10 Came close with a couple of chances but struggled to exert much influence on the game. Southampton 0 Arsenal 5 player ratings Harrison Reed - 5 out of 10 You’d be forgiven for not noticing he was on the pitch. Outshone by his opposite numbers in the Arsenal midfield. Southampton 0 Arsenal 5 player ratings Jordy Clasie - 5 out of 10 A bit disappointing ultimately and failed to impact the game much at all. Southampton 0 Arsenal 5 player ratings Josh Sims - 7 out of 10 The brightest spark for Southampton, lacked that final clinical touch but showed exciting glimpses. Southampton 0 Arsenal 5 player ratings Shane Long - 6 out of 10 Showed flashes whenever he was on the ball but never really got the service he needed. Southampton 0 Arsenal 5 player ratings Lloyd Isgrove - 5 out of 10 Struggled to really get on the ball and was subbed in the second half. Southampton 0 Arsenal 5 player ratings David Ospina - 6 out of 10 The odd slightly eccentric moment aside had a fairly quiet evening. Southampton 0 Arsenal 5 player ratings Hector Bellerin - 6 out of 10 Looked lively at times going forward and had very little to do in defence. Southampton 0 Arsenal 5 player ratings Shkodran Mustafi - 7 out of 10 Came close to scoring and was relatively untroubled at the back. Southampton 0 Arsenal 5 player ratings Rob Holding - 7 out of 10 Not an overly testing game at the back and as a result looked fairly assured. Southampton 0 Arsenal 5 player ratings Kieran Gibbs - 6 out of 10 The odd glimpse of his talents going forward and like his defensive colleagues had little to do at the back. Southampton 0 Arsenal 5 player ratings Alex Oxlade-Chamberlain - 8 out of 10 Arguably the man of the match, playing some delightful balls forward including the assist for Welbeck’s second and generally being a danger all over the park. Southampton 0 Arsenal 5 player ratings Ainsley Maitland-Niles - 6 out of 10 Solid enough but wasn’t exactly a tricky evening’s football, will face sterner tests. Southampton 0 Arsenal 5 player ratings Jeff Reine-Adelaide - 7 out of 10 A quietly efficient performance, looked good in the Arsenal midfield before being subbed midway though second half. Southampton 0 Arsenal 5 player ratings Theo Walcott - 8 out of 10 Will go home with the match ball after picking up a hat trick finishing three times from close range. An easy and satisfying afternoon for him. Southampton 0 Arsenal 5 player ratings Lucas Perez - 7 out of 10 Often anonymous, but occasionally popped up to provide crucial touches like the assist for Arsenal’s first goal, encouraging if slightly hit and miss. Southampton 0 Arsenal 5 player ratings Danny Welbeck - 8 out of 10 Enjoyed a great return to the side, scoring twice and setting up another. Arsenal fans must be praying he stays fit.

"Southampton are always strong in there so I thought the two young boys, Ainsley and Jeff, did really well beside me.

"We set the pace from the start and we controlled it at times. And when they controlled it in midfield, I thought we sat back, we were compact and we kept a good shape and we saw them out until half-time and then we pushed on from there. So I'm really happy with it.

"You get on the ball a lot and I was delighted to do that. The two boys next to me made it a lot easier tonight, they helped me out in there. When your partners are playing well it makes your life easier."

Southampton were left to count the cost of yet more rotation that left boss Claude Puel sticking to his guns over that policy.

Saints' French boss will now wait on the result of further scans on Virgil Van Dijk's foot injury before deciding whether to sign a defender in the transfer window.

Welbeck is back from a long injury lay-off (Getty)

But with time running out before the window closes, Puel knows the situation requires quick resolution.

"We'll hope to find out about Virgil on Monday," said Puel.

"And we will wait until then to decide (on whether to sign a defender).

"If I had the chance to make the selection over again, I would do the same thing."