...Champions League debut on Wednesday.
Senkerik put the home side ahead after 13 minutes when forward Stanislav Vlcek's close-range shot was deflected to him by goalkeeper Robinson Zapata.
The Romanians hit back in the 33rd when defender Dorin Goian headed in a corner kick but Belaid put Slavia ahead again in the 63rd with a shot from inside the box.
The Prague side were making their first Champions League appearance.