Play in the second round of the joint European and Challenge Tour event has been suspended due to darkness and will resume at 8am Saturday morning Portugal time although Cullen completed his 36 holes and is assured of being around for the final two rounds.
Western Australian Daniel Fox is also in 53rd position with six holes to play of round two.
Ben Eccles is at 2 under and one behind Cullen and Fox but he too has some work to do with nine holes remaining.
Richard Green has six holes to play and is at even par and currently two or three outside the likely cut line while Ryan McCarthy and Scott Arnold are further back, McCarthy also with holes to play.
Cullen, a former Australian Masters Champion with Challenge Tour status following a good season there last year, has struggled in recent starts, missing three of his last four cuts after what had been a reasonable summer in Australia.
The tournament is led by England's Matt Wallace who was a huge success on the ALPS Tour in Europe last year where he won six events.