Shaq Coulthirst headed the team into an 11th-minute lead on his first appearance for the Under-21s.
The goal owed much to Dean Parrett winning possession and driving forward. He played in Cristian Ceballos and the winger provided the inch-perfect cross for Coulthirst to plant his header into the corner.
We looked well on the way to victory four minutes later. Alex Pritchard received a quick throw from Jack Barthram on the left byline and he managed to jink inside Calum Chambers before drilling past Cody Cropper at the near post.
However, Saints responded impressively and forced goalkeeper Jonathan Miles into three fine saves, down low to his left to parry ex-Spur Lee Barnard's 20-yarder, a fine tip around the post from Ben Reeves' free-kick and then a point-blank block with his legs to deny the same player.
Reeves finally rewarded the visitors' pressure four minutes from the interval, driving through a crowded box after a corner was cleared and into the bottom corner.
The second half was somewhat cagey for the first 15 minutes and Saints levelled just after the hour, Reeves making no mistake when he was sent clear one-on-one.
We then took control for the final half-hour, enjoying passages of possession and getting into dangerous positions without creating that one clear-cut chance that might have taken us to victory.
Pritchard, a constant threat down the left, had a penalty appeal waved away in the 65th minute and Ceballos played a fine one-two with John Bostock only to see his shot blocked.
It was no surprise that Pritchard then forced Cropper into the save of the match, the Saints goalkeeper down low to his left to touch away the winger's curler that looked destined for the bottom corner.
Spurs U21s (4-2-3-1): Miles; Fredericks (Stewart, 87), Gallifuoco, Veljkovic, Barthram (Byrne, 63); Luongo, Mason (Bostock, 63); Ceballos, Parrett, Pritchard; Coulthirst. Unused sub: McGee.
Southampton U21s (4-4-1-1): Cropper; Chambers, Martin, Turnbull, Targett; Sinclair (Isgrove, 73), Stephens, Moore, Forte; Reeves; Barnard. Unused subs: Seidi, Johns, Young, Curtis.