Demichelis, who refused to sit on the bench early in the season after being dropped, came on just before the start after central defender Holger Badstuber was injured during the warm-up in Munich.
The Argentine made the best of his rare start to glance in a header from a Danijel Pranjic cross six minutes before the break to give injury-plagued Bayern the lead after a lacklustre performance for much of the first half.
"Martin showed again today that he is an outstanding central defender. He has never said he wants to leave and I have also never said it. We can talk about it when the time comes but now is not the time to do it.
"In the second half my players showed how Bayern should be playing," the Dutchman told reporters.
Ukrainian Tymoshchuk, who has hinted he would like to leave in the winter transfer window if he did not get to play regularly, fired in Bayern's third from the edge of the box and Kroos added another with a thundering long-range effort nine minutes from time.
Edson Braafheid's own goal in the 86th minute did little to dampen the champions' celebrations for their fourth league win as the Bavarians moved up with 15 points.
