Josh Thompson blazed a shot over the bar after Georgios Samaras had nodded down a Lee Naylor corner.
But Celtic remained the more dangerous, with Langfield saving from Lee Naylor and Jiri Jarosik squandering a good chance from 10 yards.
Robertson pegged one back, slamming in a deep Paul Dixon cross at the far post with Lee Naylor struggling to track back to cover.
Scottish full-back McNaughton limped off in the 18th minute after pulling up sharply with a hamstring strain and was replaced by debutant left-back Lee Naylor.
Killen put Celtic ahead after 39 minutes, heading home a Lee Naylor cross, and then fired home from a Shaun Maloney pass three minutes later.
Vennegoor of Hesselink beat the offside trap in the 17th minute only to drag his shot wide and the Dutchman then headed wide from Lee Naylor's corner.
But Lee Naylor has been such an astute purchase that surprise has been expressed that the former Wolves man has not made England's troublesome left-back position his own.
BBC: SPORT | Football | My Club | Celtic | Celtic's title relief
Nathan Dyer cut inside Lee Naylor from the right-wing and teed-up Emnes but the on-loan Dutchman from Middlesbrough fired his shot at the diving Hudson from 10 yards.
Few among the visiting support would have predicted that Celtic manager Tony Mowbray would hand China captain Zheng Zhi his debut, while Lee Naylor made his first start of the season.
Fortune looked certain to level with just over quarter of the game remaining after a Lee Naylor free-kick broke to him in the box, but his left-foot finish was deflected behind from four yards.
Celtic's latest recruit Fox will vie with Lee Naylor for the left-back role and the Celtic manager knows the former Wolves defender has received criticism from sections of the club's support in the past.
The Celtic manager made tactical changes in the second half in an attempt to break the deadlock, first removing Aiden McGeady and Scott McDonald for Lee Naylor and Marc-Antoine Fortune, then throwing on Niall McGinn for Robson.
In bright sunshine, the present side, managed by Neil Lennon, ran out easy winners with a Lee Naylor hat-trick, doubles from Gary Caldwell and Scott McDonald, and with Jan Vennegoor of Hesselink, Aiden McGeady, Massimo Donati and Simon Ferry also on the scoresheet.
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