The Bees were beaten 3-1, with Bryan Mbeumo putting the visitors ahead inside the first minute before Spurs won via goals from Dominic Solanke, Brennan Johnson and James Maddison.
Frank later said: "I'm very pleased with the performance, I think we did a lot of good things. We had four good chances to create the equalise before the goal from Maddison.
"We need to take those chances if we want to get something here, Playing against a very good team who have performed well over the first four games. Today they probably raised their level a bit, plus they got the small margins and the momentum and then they are difficult to play against.
"We are playing against a team whose end stand is bigger than our stadium in terms of capacity. That shows the difference. No complaints.
"It's my job to put a competitive team out there but it doesn't help when we have five potential starters out."
On Spurs goalkeeper Guglielmo Vicario handling the ball outside the box, he added: "It wasn't impacting the game. It wasn't a penalty, it wasn't a red card, it was just a free-kick outside the box which John (Brooks, referee) should have seen. I think he refereed a very good game, that was just a small little thing. If you come here you need to get everything with us to maximise our chances in the game."