The Swiss champions trail the reigning Champions League winners 2-1 in the Europa League semi-final following the first leg at St Jakob-Park last week but Yakin is going into the return bout with plenty of confidence.
"Every game is difficult and we know we're playing against Chelsea, who are the Champions League winners. They have two top players in every position,” he said.
"But we will do everything. We will be brave, we'll play with confidence and who knows? Maybe we can achieve a small wonder and we can qualify for the final."
He added: "We've got to be clever, we've got to be intelligent.
"We've also learned that if you always have possession it doesn't mean you're going to win the game.
"We have to see what we can do, be confident and try our best."