Following on from back-to-back wins in the Bundesliga, the Royal Blues now appear to have found form at just the right time ahead of a busy period of fixtures.
"We've made a sensational start to the Champions League," said Keller, whose side only just sneaked into the group phase with victory over PAOK Salonika in the play-off.
"We've kept another clean sheet and I'm absolutely delighted about that. We were patient and created numerous chances.
"I'd say we were dominant in winning this game. Maybe the first goal was fortunate, but sometimes that's just what you need."
Atsuto Uchida's mis-directed cross put Schalke ahead with goals from Kevin-Prince Boateng and Julian Draxler completing a resounding win.
Draxler admitted things "are always getting better" for Schalke while lauding his growing understanding with Boateng.
"To keep three clean sheets in a row is excellent," he said. "I was able to tee Kevin up once today and we are combining better and better, more harmoniously.
"I think we're heading in the right direction."