Ok Oldie .......... take out the door frame........ also the half bricks in the reveals, so that you can "tooth-in" to the existing.
Look at the bonding of the brickwork where it breaks out above the lintel, and try to copy it ............ I guess you're leaving the lintel in?
If it's your first time, don't try to rush it. If you're not finished, just board it up temporarily.
Matching the mortar colour is the hard part. Try and get the same colour sand, and, if the mortar is looking old and discoloured, you could put a little black mortar dye into the mix .............. hope it works out :o)