And, when Newcastle did catch a backtracking Bolton out with a pacy attack after clearing a corner, Joey O'Brien cynically brought down Jonas Gutierrez.
Substitute Emmanuel Eboue quickly added the fourth as Arsenal launched a sweeping counter-attack from a Porto corner, Arshavin again making life easy for his team-mate to go around Helton and score.
McFadden converted and a second try followed for the hosts on the stroke of half-time, with replacement Eoin Sheriff stealing a Warriors' lineout to launch a swift attack which ended with Dempsey crossing in the corner.