But Jack pushed through to take over the lead on the fifth lap of six and the Jack-Mobberley combo maintained that position until the end, eventually winning the race by a little over 30 seconds.
Auckland's James Ainsworth and Daniel Nieuwenhuyzen held third place in the race until lap four when 14-year-old Auckland rider Jake Wightman, straight from his junior win at the Dirt Guide Series near Tokoroa the day before, powered past him to snatch away third spot.
Wightman's team-mate, James Mancer (Yamaha YZ250), extended the lead and the young team eventually claimed third overall by four minutes.
Round two of the Spectrum Woodhill Two-Man Cross Country series is set for Sunday, August 31, with the third and final round due on Sunday, September 28.