Russell Martin believes Southampton’s heavy defeat at Sunderland is evidence that his side have not yet shaken off the hangover of last season’s relegation from the Premier League.

Saints suffered their first defeat of the Championship campaign as they were hammered 5-0 by the brilliant Black Cats at the Stadium of Light.

Martin’s side endured a horror start, going behind to Jack Clarke’s opener after just 52 seconds before Pierre Ekwah added a second for the hosts six minutes later.

Southampton then attempted to get some control of the game but conceded a third on the stroke of half-time, when former West Ham midfielder Ekwah hit his second.

Bradley Dack added a fourth immediately after the restart before 16-year-old substitute Chris Rigg rounded off the rout deep in stoppage time.

Martin said: “I feel really sorry for the supporters that came, they were amazing right to the end and we have to make sure this is the toughest day we have and we have to learn from that.

“Initially it’s really difficult to analyse because I’ll have to watch it back, but when you concede two goals early it completely changes the complex of the game.

“The one thing we spoke about is starting well. It’s a young team at Sunderland and when the wind is in their sails they’re very good but when they have a difficult start they can then find it tough to get the game back

“But the game just went for them. They had momentum after their start, brilliant momentum and we didn’t have enough of that.

“Everything they did well – they fought, they came out on top of duels, they worked so hard – we didn’t, we went in self-preservation mode, which I think is still a hangover from last season.

“It’s the first defeat but the manner of it really hurts.”

The win extended Sunderland’s unbeaten run to three games and Tony Mowbray was delighted after what he says has been a “tough week” off the pitch due to transfer speculation surrounding a number of his players.

The Black Cats lost Ross Stewart to Southampton on deadline day but also had interest in a number of other key players, including Ekwah, Clarke, Patrick Roberts and Dan Neil – who all stayed at the Stadium of Light.

Mowbray said: “The result is important for the team and the spirit.

“It’s been a tough week in the build-up to it in terms of speculation around a lot of our players. In training yesterday, there were rumours about certain clubs looking at certain players and it disrupts young footballers.

“I can see them talking to each other, and yet they showed great professionalism today. We all turned up and did what we hoped we could do.

“I’m happy with the day and happy for the fans. On paper this is a really difficult game. I looked at their squad on the back of the programme and just saw name after name after name of really experienced high quality footballer.”

Sunderland made four deadline-day additions, including the loan signing of Chelsea forward Mason Burstow.

Mowbray said: “We have some extra attacking players now and they might watch that game today thinking how do they get in that team, but that’s OK because competition drives all footballers.”