I would have thought it worth the shot. Afterall on an international itinerary you get lounge access along the way as long as they connect. So if both tickets were on points you should be fine. Otherwise I would just walk up smile and say that you havev arrived on an international itinerary with another *A airline and how much you are looking forward to getting home, long flight and all, and you should be in.

Someone else will quote the exact rule, but whatever I would still give it a go.

I take it is in a different terminal to the SQ Raffles lounge as that could also be worth a try?

Mark