The 6ft 4in forward is eligible to play for England, having been born in Devon but qualifies for Scotland through his father. He has played for his adopted country three times but his performance at home to the Barclays Premier League leaders suggests the Scottish Football Association might have a fight on their hands should their English counterparts have designs on the 18-year-old.
As well as winning three caps, Gallagher has been part of several training camps arranged by the SFA. Hampden officials, however, are well aware that the young striker can still switch allegiance until he plays a competitive match for Scotland.
Pochettino has no doubts that Gallagher has a bright future which might just be good news for Gordon Strachan. He said: "He had various chances to get on the scoresheet and wasn't able to do so but overall he had a great performance and that his progress is coming up to standard. He's doing really well and progressing as we want him to. We put in Sam to make his full debut and we had full confidence that he was going to do well because we know him and we have been working with him for a year, so there was no gamble. He is just another example of the great work that the academy is doing.
Mark Wotte, the SFA performance director and former Southampton youth director, was also delighted to see Gallagher in the first team.
He tweeted: "Well done Sam Gallagher for Saints FC starting such an important game. Southampton again the perfect example for superb talent management!"