Moss produced a string of fine saves in the second half at Stevenage to thwart Colin Calderwood's young guns and maintain the Saints' 2-1 half-time lead.
Goran Bunjevcevic played his first competitive 45 minutes after a recent thigh strain as we ended with our youngest reserve line-up so far this term - John Piercy was the elder statesman of the side at just 22 with goalkeeper Gavin Kelly and striker Yannick Kamanan as the only other players to have hit 20.
A scrappy opening period produced a couple of efforts wide at either end, Sutton going close, before the influential Piercy forced the first save of the half, Moss getting down to turn away a low drive from 25 yards.
Home stopper Gavin Kelly had to be on his toes to deflect Ashford's shot wide after 24 minutes but he was helpless as the visitors took the lead 10 minutes later.
It was a disappointing goal from our point of view. Goran Bunjevcevic's free-kick was intercepted, Saints broke quickly and McDonald's burst into the box was halted by O'Donoghue's challenge. The referee pointed to the spot and McDonald made no mistake.
To their credit, the youngsters hit back within seven minutes. Good possession led to Piercy's free-kick falling at Bunjevcevic's feet only for his volley to be headed off the line by Baird but from the ensuing corner, Galbraith latched onto a loose ball on the edge of the box and the winger dispatched a rasping shot into the bottom corner.
Kelly saved well again from McDonald but Saints grabbed the lead again just before the break.
This time McDonald was fouled on the edge of the area, Kelly got down well to parry Baird's effort but Gray was on hand to bury the rebound.
Ron Henry replaced Bunjevcevic at half-time and both teams were on the front foot after the break as Kamanan and Piercy tested Moss.
The Saints keeper produced the save of the game on the hour as Herron lofted back a clearance and Kamanan's looping header was turned over the bar at full stretch. But he was nowhere from the corner and Henry's stabbed volley at the far post was hacked off the line by Baird.
Moss soon redeemed himself to save at full stretch after Piercy had cut in from the left, beat three players and attempted to curl into the far corner in the moment of the match.
And Piercy was there again to instigate the final assult in the 88th minute. The skipper and inspiration of the side found Snee with a pinpoint 50-yard crossfield pass, Snee took it superbly and beat the last man only for Moss to save the day again with his legs.
Spurs Reserves: Kelly, Consorti, Herron (Hughes, 72), Bunjevcevic (Henry 45), O'Donoghue, Bowditch, Snee, Piercy, Galbraith (Marney, 68), Sutton, Kamanan. Subs: Jalal, Noto.
Southampton Res: Moss, Baird, Benali, Bleidelis, Monk, Gray (Williamson, 68), Chala, Ashford, Delgado, McDonald, Howard (Caceres 64). Subs: Bevan, Crowell, Wallace.
Our reserves proud unbeaten home record finally came to end at the hands of a fine display from Southampton goalkeeper Neil Moss on Monday night.