Victory over Villarreal was achieved thanks to an early own goal at Tottenham Hotspur stadium.
Frank, on his European debut, remarked afterwards: "I thought it was a big win. In any competition it's good to get three points and get a good start. I'm happy with that. I'm happy with the clean sheet. I'm happy with the defensive side of the game. I think we were extremely good and limited Villarreal to very little throughout the game. They were a good team I really admire.
"Obviously, offensively, we struggled on the day to create something against a good team. They also defended very well, which we knew in the 4-4-2 structure. They were very aggressive. When we were on the day, I think, they needed the highest level in terms of touch, passed and decision-making, and they nailed that.
"Then it was a very even game that we edged in the end. What I like is that our foundation is strong. Now we are four games won, three in the Premier League, one in the Champions League, and we have four sheets, which is massive.
"Obviously, we are building the offensive structure more and more. Xavi Simons has just come into the club. It's fair to say he and Djed (Spence) need a little relationship, of course, to get going.
"No complaints, it's just natural. I think there was a spell in the second half where we decided to give the ball away every single time we had it. We gave the ball away, let's bring it back. Oh give it away, let's bring it back. Of course, it's a little bit easier to sit here with a smile, but of course, at that level, we will raise of course."
The Dane also said, "The Champions League is unbelievably tough. It was a very good team we faced today. And managed to get out of a very tight game as winners. With that feeling that you fight and run and you do a lot of things as a group together, and then get out on top and win, it's exceptionally good. It just builds that extra foundation, extra layers. And sometimes you can't hit the highest level, and still get away with a win, in an even game, I think it's fantastic."