Gallas failed to last until half-time with a recurrence of his calf injury and another blow arrived just before half-time when Fabregas was harshly booked for tangling with Busquets.
But the Blues had also seen one of their inspirational players drop by the wayside, with captain and Lions prop Gethin Jenkins succumbing to a calf injury at half-time.
The visitors dominated the opening stages, with England centre Riki Flutey, playing at fly-half after missing the autumn Tests with a calf injury, Powell and flanker Richard Birkett, back for his first match since October, all prominent.