Flying into Beijing, leaving by ship to Japan.

I am an Australian flying Singapore- Beijing and the next day leaving Beijing (Tianjin port) to Okinawa, Japan on a cruise shi.. Am I eligible for the 144 hour transit on arrival? Some sections on this site say one must leave from the same airport as one arrives in. But I won't actually be leaving Beijing, just going from airport to seaport.
Thanks in advance... the website is a bit confusing and with the national Day holidays my time is extremely limited (I depart Australia Friday 5th Oct.). :-)