Revenge for a handball equaliser? FA Cup progress? A chance for a warm welcome to a new club record signing? No, this game was all about momentum for Saints.

In sport, where momentum is so crucial, Saints went into the fourth round tie with Watford knowing they needed to increase a feeling of wind at their backs.

The game was much less about making it to the last 16 of the FA Cup, though that is a handy by-product of victory, and more about preparation for a vital Premier League double header.

The fixtures against Brighton and West Brom in the coming days could go a long way to deciding whether Saints will stay in the Premier League.

And Mauricio Pellegrino knew he had to try and keep the wheels moving after a creditable draw with Tottenham, which suggested things were still edging in the right direction.

Pellegrino’s team selection – really going as strong as he could – proved that.

There would have been an argument for resting players to protect them for that crucial double header. When Ryan Bertrand, such a key man for Saints, limped off you did wonder whether he had made the correct decision.

But the plan ended up coming good. Victory makes everything seem so much better in football, and a first home win since November, no matter how it came, was exactly what was required ahead of the visit of Brighton to St Mary’s.

Saints carried forward their momentum from the Tottenham game to get off to a fast start and take the lead after just four minutes.

It came via a set-piece with Bertrand delivering an outswinging free kick from the left wing that came to Shane Long.

The striker looked set to score but his low shot was saved by the legs of Orestis Karnezis. It ricocheted straight to Jack Stephens who gratefully dispatched the chance with a simple low finish from close range.

Saints spent most of the first half on top, albeit in a fairly pedestrian game, but unable to add to their advantage.

Cedric Soares was at the heart of most of their most potent attacks.

He might have scored himself had Jose Holebas not done just enough to put him off as he lined up to shoot after Long’s brilliant left wing ball, while the Portuguese delivered a right wing cross that was just too high for Long to direct on target.

The right back had a go at goal on 26 minutes but his swerving low drive was saved by Karnezis before a superb low ball into the six yard box somehow evaded everybody and went behind.

Watford only threatened Alex McCarthy in stoppage time when Richarlison spotted him slightly off his line and tried an outrageous effort that the keeper was able to tip over.

The rather average feel to the game as a spectacle continued into the second period, but again it was Saints who were certainly the better of the two sides.

Long forced Karnezis into a save and then pulled off a marvellous touch to bring the ball under control in the area before a shot to forget.

Pierre-Emile Hojbjerg produced a wonder strike from 25 yards out, hitting a fierce right footed shot that moved in the air before rattling the crossbar and bouncing to safety.

After Watford had thrown on the ammunition to attack and to potentially go more direct, which undid Saints in the second half at Vicarage Road, Pellegrino responded.

It wasn’t a move that went down well with the Saints faithful as he took off an attacking player in Boufal for Maya Yoshida and went to three centre halves. At Watford he had dropped Oriol Romeu deeper instead.

While switching to a more defensive mode again didn’t ease the nerves, it did work out this time.

Watford were missing Troy Deeney, and that lack of quality did them no favours as their attempts to get back into it looked more desperate than targeted.

They also weren’t helped by their supporters, who chanted some pretty negative stuff about their own team throughout the match, and the sparks that flew as players became embroiled in arguments with fans after the final whistle summed it all up for them.

They look frayed, and in big trouble.

Stefano Okaka did hit an acrobatic volley over the bar, while right at the death Watford created their best chance of the game as Christian Kabasele missed the target with a free header at the far post ten yards out.

But with momentum so critical it felt as if it was Saints edging in the right direction and Watford going the wrong way.

If Pellegrino’s men can keep this going they might just be able to ease their relegation fears in the coming days.