Hasenhuttl was pleased with how the youngster never dropped his head.
Hasenhuttl said: “It was not easy I think but in a few moments he showed that he is definitely, in the 10 position, an alternative.
“He caused more threats than the other 10s in the moment.
“This is where I really get what I expected - that he doesn't decide a game immediately. It was also not so surprising.
“But he had the chances to do it. I think he must work on his finish - it can be better.
“And physically, the Premier League is a high level."
Tella's form was rewarded when he penned a fresh deal at St Mary's last July, keeping him at the club until at least 2023.
His first league start came during Saints' miserable run of top-flight form, which has now stretched to one point from a possible 24 in the division.
Asked whether the promising forward had the mentality to step up for Saints during this difficult run, Hasenhuttl replied: “He's not afraid of going in the duels – in the one-against-one.
“He takes responsibility and this is what you have to do as a young player and the rest you learn."