Halliday's opener came in the 44th minute when the Glens man contorting himself superbly to hook the ball home after a frantic scramble in the Linfield six-yard box involving Willo McDonagh and Darren Lockhart.
Right from the start, Chelsea looked off key and when skipper John Terry failed to head away Paul Konchesky's cross, Gera was on hand to hook the ball in after Bobby Zamora had nodded it his way.