Carlos Vela starred for Real Sociedad as they ensured Michel's tenure as Sevilla coach began with a 2-0 defeat.
Michel was appointed last week after Marcelino Garcia was sacked following their 2-1 loss to Villarreal, and he saw his new charges fall behind to Vela's 64th-minute strike.
The on-loan Arsenal man then set up Ruben Pardo for his side's second four minutes later as they leapt above their opponents in the Primera Division table.
Former Real Madrid star Michel must now ponder a relegation battle with Sevilla three points above the drop zone following three straight defeats.
Vela gave warning of what was to come in the 13th minute when he hit the post from inside the area.
And it was Sociedad making much of the running as Xabi Prieto nodded Pardo's corner wide from six yards and Imanol Agirretxe's header was held by Andres Palop.
Pardo fired wide, before Alvaro Negredo sent a rare Sevilla chance over the bar from 12 yards on the half-hour mark.
Manu was also wasteful for the visitors, but it was Vela who again had them worried when Palop produced an excellent save four minutes before the break to keep out the Mexican's close-range strike.
Sevilla came out looking livelier after the break, perhaps after some choice words from their new boss, with Jesus Navas and Negredo both missing chances.
But Sociedad deservedly went ahead just after the hour when Vela latched on to Prieto's cross from the left and fired home.
Vela then turned provider as his pass found Pardo to finish from 20 yards.
That all but killed Sevilla off and, indeed, it was Sociedad who went closest to adding to their tally when Antoine Griezmann's strike was saved by the feet of Palop.