Jan Bednarek gave Saints the lead before Alexander Isak struck twice, one from the penalty spot, and Sandro Tonali also scored for the 3-1 win at St Mary's.
Juric said afterwards: "Yeah, I think we gave everything that we got and it was some crucial moment like a penalty and that was in a really good moment. It's not easy to play against Newcastle, but it wasn't enough.
I"t was a crucial moment, a penalty I think. For me it wasn't a penalty, it was in a very good moment for us. We scored a goal and we moved the ball well and this moment I think changed the game a little bit.
"I just saw it after the game and for me it wasn't a penalty.
"We have to say that the second goal, I saw the technical quality of the Newcastle player, incredible. Sometimes you have to accept this, the pass, control, shoot, it was like really good quality, high quality."