A double strike from Omer Riza - in probably his last game for the club - and one from youngster James Allen rounded off an impressive season for the second string.
Roger Cross is out in La Manga with the first team players as they earn a short break away, so Tony Carr and Paul Goddard looked after the team, and Paul says: "It was a very good display against a much more experienced Southampton team.
"The boys applied themselves very well, dug deep, and scored an early goal through Omer after a long ball from Raggy."
Omer will be leaving in the summer, but Paul adds: "He has applied himself very well throughout the season. He has got electric pace, and tonight he used it to the best of his ability.
"But we had to defend a little bit and the boys did really well with that, and as the second half went on we got stronger and stronger.
Omer scored the third goal as well, with youngster James Allen scoring in between.
"James is having a taste of reserve team football which is a lot more physical and quicker than he is used to. At times he gets caught out with that but he has certainly got a lot of ability on the ball - but he has got to learn how quick and sharp the game is," says Paul.
"He has certainly got the ability and now it is how he applies himself to playing reserve team football."
Paul says the scoreline of West Ham's last reserve game of the season could have been higher and adds: "It could have been a lot more - it was very good."
Izzie Iriekpen and Glen Johnson, who both were in the senior squad for the trip to Newcastle on Saturday - Izzie was on the bench - both played their part in the win and Paul adds: "Izzie had a sound game at the back alongside Raggy, who did well, and Glen had a sound game at right back."
Also involved was Adam Newton, who is thinking over a one year offer at Upton Park, and Paul says: "It is up to Adam now to decide where he thinks his future lies. He has had that spell at Orient and a few other clubs are interested in him.
"He has had talks with Glenn and there are opportunities here for him as well."
Team: Andersson, Johnson, Iriekpen, Soma, Lumsden (Eastwood), Newton, Byrne, Carrick (Ferdinand), Allen (Ward), Riza, Mehmet. Subs unused: Jackson, Smith.