Jan Poortvliet made just the one change with new loan signing Ryan Smith coming in for Chris Perry. This meant Paul Wotton moved back into the centre of defence and Drew Surman into centre midfield.
It was a curious decision to leave out our most experienced defender given Watford's trademark organisation at set pieces and Saints paid the price, gifting them three identikit goals, with Saints failing to clear the second ball each time.
In truth it should be no surprise with two midfielders in the back four, alongside two youngsters in their first ever season. Svensson's knee and Saints' failure once again to sign defenders on loan are proving hugely costly.
Despite the scoreline, Saints looked good in the centre of the park as Surman and Cork stroked the ball around with ease. The less said about what happened in front and behind them the better with a collective lack of organisation that the manager has failed to rectify.
Up front Saints somehow managed to miss two penalties, the first an unforgivably casual McGoldrick penalty, and waste a simple one-on-one and a potential open goal with the keeper stranded and Robertson opting to shoot from an impossible angle rather than pick out a team-mate.
On the Cross verdict
Even by Saints standards, it was one of the strangest first halves witnessed at St Mary's. Saints looked well in control and could have been 3-0 up at half time if they could simply defend set pieces and take the simplest of chances.
However, those basics though look big asks on today's performance. Saints' naivety in personnel and organisation is coming home to roost with seemingly no lessons learned after the drubbing away to Coventry.
It was a concern to see Jan Poortvliet in Steve McClaren England mode looking out of his depth, motionless on the touchline and unwilling to make positive changes to influence events unfolding in front of him. The contrast with the bundle of energy that is Aidy Boothroyd was telling as he geed up his players and got them organised.
Watford did their homework targeting Saints at set pieces and marking Saints' main attacking threat, Adam Lallana, out of much of the game. Even they though couldn't have expected a Saints side short of confidence to be so wasteful in front of goal.
The side badly needs leaders, especially at the back, but also in central midfield. Surman is rising to the challenge and took up the mantle in midfield, but he needs a bruiser alongside him and at least two behind him to shake up the opposition and ensure full concentration from those around them.
Unfortunately, the two most likely candidates at the back, Thomas and Svensson, are in the treatment room and Saints urgently need to look to the loan market to secure an experienced centre half and a full back to shore up such an inexperienced defence.
Until these defensive failings can be addressed, Saints are going to keep getting punished no matter how pretty the football in the middle of the park.
Ahead of this game Poortvliet spoke of targeting six wins in the next ten. After today, that target seems as naive as the performance itself.