Always chasing the game, Danny Rose and Kyle Fraser-Allen (pictured) levelled the scores at 1-1 and 2-2 but Pompey grabbed the winner as both sides pushed for victory.
"We're keen not to hide behind excuses but we were without Alex Olsen, Yuri Berchiche, Adam Smith, Dean Parrett, Andros Townsend and Yaser Kasim through a combination of injury, illness, international duty and suspension," reported coach Alex Inglethorpe.
"However, that gave an opportunity for some other lads to come in and have a game including Josh Ekim and Jake Nicholson from our Under-16s.
"We started brightly enough but then started to fade a little. We had a lot of the ball but didn't make use of it as we have in recent weeks.
"We fell a goal behind just before half-time but managed to hit back after 55 minutes following a good individual break from Danny Rose, he gambled on a ball over the top, got onto it and scored.
"Unfortunately, we conceded shortly afterwards but equalised again after 70 minutes after a cross from the right from Danny found Kyle Fraser-Allen at the far post and he managed to control and bend it into the bottom corner.
"However, in pushing forward for the winner, we got caught out ourselves and that's unlike us, we haven't conceded that many goals this season and mentally, I think we surrendered a bit too easily.
"There won't be many times in the lads' career that they will be able to say they've won 10 league games on the trot. Obviously going away last weekend and reaching the final of major youth tournament was a real high but coming back and losing is a low."
Spurs U18s: Jansson, Mtandari, Hutchins, Cox, Shehu (Asajile, 46), C Butcher, Fraser-Allen, Ekim (Davis, 55), Obika, Mason (Nicholson, 80), Rose. Unused: Dalton.
Our Under-18s' fantastic winning run finally came to an end against Portsmouth on Saturday.The lads had strung together 10 wins on the trot in the FA Premier Academy League dating back to November - their last defeat was at MK Dons in October.