Claude Puel lavished praise on his £17million January recruit Manolo Gabbiadini after he scored twice as Southampton ran riot at the Stadium of Light.
Sunderland dominated the early exchanges but couldn't capitalise on their pressure, with the Black Cats failing to carve out any clear openings.
Southampton made them pay, Gabbiadini opening the scoring after 30 minutes in controversial circumstances.
The Italian striker put the ball past Vito Mannone with his arm but neither referee Paul Tierney or his assistants spotted the offence and the goal stood.
Gabbiadini then got the better of Lamine Kone and John O'Shea in added on time to double Southampton's half-time lead with a low, smart finish past Mannone.
David Moyes made changes in an effort to rescue the game, but Jason Denayer's late own goal and a fourth in stoppage time from substitute Shane Long completed a miserable afternoon for the home side.
It seemed inevitable Gabbiadini would score, given his namesake's legendary status at Sunderland.
Asked about Gabbiadini's start to his career in England, which now amounts to three goals in two games, Puel added: "It's a good start, a very good start, of course.
"He is a technical player.
"You can find him between the lines because he has quality, good control, good passing."
Puel was delighted with his team's display - which earned just a second league win in eight attempts - and will now hand his players four days off before beginning preparations for their EFL Cup Wembley showdown with Manchester United on February 26.
Puel said: "It was a fantastic game and good, of course, with all those games lost before, it was very important to react and to give a good answer.
"I hope it's the first game of a good cycle of course.
"It was important to win this game, a fantastic performance. Now we will take four days off with the family because we deserve this with all these games.
"It's a good thing to do it after the win and then we can prepare for the next game, a little game.
"This game, we know, is a fantastic, exciting game. We are not favourites, of course, but we know that in football, all is possible - we saw this against Liverpool.
"To win with this result, four goals and with a clean sheet, it's very good for the confidence and good preparation also for this game."