"First of all it is important to qualify - being first or second in the group, last season proved that means nothing," he said.
"We have to qualify, and to qualify soon is better than late.
"The important thing is that we have what is good - a victory at home and a draw away. We are in a good way. But we cannot allow ourselves to sleep."
Chelsea are level on four points with Liverpool, who head the group on goal difference, while Betis are on three points.
Betis lost at home to Liverpool in their first game, but beat Anderlecht last time out.