Hi guys,
singing along this song while keeping the rhythm straight it's driving me crazy

I can play this song flawlessly on the original record or on the Justin version, I just can't get past the first verse while singing.
What I usually fail to do is the push (change on the 2&) from G to A while singing (except, as I said, for the first verse which it seems I can nail it for some reason).
Maybe someone who managed to overcome the very same challenge has tips to share...