Saints used the match as an opportunity to give some fringe players one last test before the start of the npower Championship season, with the rest of the squad made up of youth players and a couple of trialists.
One of those looking to impress was full back Anton Blackwood, but his involvement was brought to an untimely end after just 15 minutes as he succumbed to a knock in the opening exchanges.
Jessy Fusu in midfield also didn't make it to half time as manager Martin Hunter was forced into some tactical changes following an unbelievable 5 minute spell where the hosts scored three times which stunned the Saints side.
The first effort came from the penalty spot which was rightly awarded following Aarran Racine's foul on Ryan O'Hara. Jamie Slabber sent Forecast the wrong way on 20 minutes to open the scoring.
Two minutes later, the Spitfires doubled their advantage when Andrew White broke through the middle to dink the ball into the bottom corner.
Hot on the heels of that strike was a bizarre third goal that saw defender Danny Smith head home Forecast's punched clearance into an unguarded net from all of 20 yards.
Saints earned a reprieve before the break when a weak clearance at the other end was pounced upon by winger Lloyd ISGROVE who kept his cool to finish from inside the area to reduce the deficit.
After the break, White went close to a second when he smashed a shot against the cross bar which half time substitute Jack Dovey could do nothing about in the Saints goal.
At the other end, Jonathan Forte tested the hosts' 'keeper with a low strike, before the Spitfires restored their three goal margin when Slabber was brought down by Harlee Dean inside the box, and the striker stepped up himself to convert the spot kick.
Saints went closer late on through a Lee Holmes free-kick and a Sam Hoskins header, but a below par display all round from the visitors will have frustrated those watching on including First Team Manager, Nigel Adkins.
Eastleigh: Mike Green, Andy Forbes, Frankie Raymond, Danny Smith, Tom Jordan, Billy Tsolovos, Jordace Holder-Spooner, Ross Bottomley, Jamie Slabber, Andrew White, Ryan O'Hara.
Saints XI: Tommy Forecast (Jack Dovey 46), Anton Blackwod (Jack Saville 15), Ryan Dickson, Andy Robinson, Aarran Racine, Harlee Dean, Lloyd Isgrove (Alberto Seidi 70), Jessy Fusu (Sam Hoskins 30), Jonathan Forte, Lee Holmes, Joseph Mills (Jason McCarthy 60).
Attendance: 804
Martin Hunter felt that the hosts deserved their victory, and says he was let down by the performances of his players on the evening.
"The expectations of Southampton Football Club were not seen or met, and we got exactly what we deserved," he lamented.
"I'm bitterly disappointed, and very annoyed. There were one or two home truths told at half time and we've been outfought, out battled, and outplayed.
"We couldn't adapt to their intensity and their willingness to work hard, and that is not acceptable from any of the players that played, no matter what their experience or inexperience's, you have to earn the right to play the game, and we didn't in either half.
"I said to Iain Baird after the game that they deserved to win and they did. The performance from ourselves was poor however you look at it.
source: Saints fc