We spoke to West Ham correspondent Dave Evans from Recorder Newspapers to get the view from the opposition ahead of the Hammers' visit to St Mary's...
How would you sum up West Ham’s season so far?
It has certainly been a season of ups and downs. With a brand new manager in Manuel Pellegrini and over £100million spent on new players, expectations were really high amongst West Ham fans.
But things could not have started much worse and they were hammered by rampant Liverpool on the opening weekend and then proceeded to lose their next three as well, including a home defeat by Bournemouth, leaving them bottom of the Premier League.
They suffered some big injuries too, with Manuel Lanzini and Winston Reid still to play this season, and the likes of new boys Carlos Sanchez, Jack Wilshere and Andriy Yarmolenko on the treatment table.
A vital win at AFC Wimbledon in the League Cup gave them some confidence and their first away win of the season at Everton helped to turn things around and recently they have been in superb form.
They beat Manchester United at home, drew with Chelsea and despite a thumping home loss to Manchester City, they have found some great form.
Going into last Saturday’s game with Watford, they had won four on the trot and sat ninth in the table. From that awful start, that is a pretty impressive record.
What changed to spark the winning run?
The fixture list has certainly helped. Their four wins on the trot were all against teams below them in the Premier League and Manuel Pellegrini seems to have instilled a new style of play into the side.
They are now playing with two strikers as well as two wingers in club record signing Felipe Anderson and Scot Robert Snodgrass, who have been in fine form.
Add to that a strong defence with new boys Issa Diop and Fabian Balbuena striking a fine centre-back partnership, plus the continued excellence of youngster Declan Rice as a defensive midfielder.
They seemed to have found the right formula, despite losing star striker Marko Arnautović to injury recently.
How have West Ham overcome injuries to key players, and who has stepped up in their absence?
It has certainly not been easy as some of the injured players have been key men. Manuel Lanzini is a huge miss, Andy Carroll has only just returned to fitness, while since the start of the season Carlos Sanchez and the impressive Andriy Yarmolenko have been ruled out for most of it.
However, the manager has managed to fill those gaps and inspire the rest of the squad.
Robert Snodgrass has been the biggest success story. On loan at Aston Villa last season, he has come back, was told to lose weight and has made himself an integral part of the team with goals and assists.
Felipe Anderson had a rocky start to his West Ham career, but is now flying and is top scorer with six goals, while the spirit of the whole team seems to have been transformed under Pellegrini.
What are the main differences tactically under Pellegrini?
There is a huge difference from the guidance of David Moyes last season, whose first instincts were for defence rather than attack.
Moyes did the job he was brought in for, to keep the team up, but Pellegrini has taken them to the next level.
His style is to try and win every game, to act as a big team and to play away from home in the same way they play at home.
He plays four at the back, compared to the five that Moyes employed, as well as two wingers.
He has also played one or two strikers, with the current option being for the latter. It is certainly working at the moment.
dave evansmoyes did the job he was brought in for, to keep the team up, but pellegrini has taken them to the next level.
Is the club finally feeling at home at the London Stadium?
There are always going to be some detractors, supporters fear change, but on the whole things are going really well at the London Stadium.
They have played to full houses in every home league game and to hear the noise and atmosphere in the place in their recent game with Crystal Palace was tremendous.
They have just agreed to increase their capacity to 60,000 in the New Year and they are almost certainly going to fill that as well.
What do you expect from the game at St Mary's?
Southampton are clearly hungry for points under their new manager and will have got a huge confidence boost with that win over Arsenal.
Charlie Austin often has a good match against the Hammers and Saints’ recent record against West Ham is a good one.
However, West Ham are on the top of their game and proving clinical in front of goal at the moment, so if they get their noses in front, the pressure will certainly be on Southampton and the Hammers could well take the points.