IDW Publishing's digital comic, the first title to be released in single issues through the storefront, is currently outselling Scott Pilgrim to hold on to the number one spot.
Children's Bible: Comic Book Parables and Miracles occupies third place, with two volumes of Brian Michael Bendis's New Avengers rounding off the top five.
IDW's Star Trek/Doctor Who crossover, written by Scott and David Tipton with artwork by J.K. Woodward, got under way earlier this week.
The story sees the Doctor and his companions team up with Captain Picard and his crew to take on a combined threat from the Cybermen and the Borg.
Star Trek: The Next Generation/Doctor Who: Assimilation2 #1 is available via the App Store for £2.99.