Mockford was limited to just 24 minutes due to foul trouble, and Andy Lawrence was the only other Brit in double figures with 14 points. However he we will want to improve his three from 15 shooting from the field, while Patrick Nyeko added nine points for the British side.
Will Neighbour had a good night on the board, adding three blocks to his seven rebounds, while Lawrence added three assists and as many steals. Anders Stien led the Norwegians with 19 points.
The game had started well for GB, with Nyeko opening the scoring, and a Neighbour jump shot plus a second Nyeko basket putting them 6-5 ahead.
Colin Sing made it 8-5 with three minutes gone, and although Stien gave Norway their first lead of the game, Neighbour hit another jumper to give Britain a 10-9 lead with four first period minutes remaining .
Neighbour scored his third basket of the game on the 2:46 mark, but that proved to be Britain's final lead of the game, and a Magne Fivelstad jump shot sent Norway into the final break with a 13-12 lead.
Fivelstad opened the second period scoring with a pair of free-throws, and it took until the 1:27 mark before Lawrence ended and 11 plus minute drought for GB with a pair of free-throws.
By then, however, Norway had rattled off 20 straight points, and although Aki Fullah doubled Britain's tally for the period off a Josh Rolls-Tyson assist, GB went into the locker room trailing 34-16.
There was no way back for Lewis' team after that, but they did restore some pride in the second half - being narrowly outscored 20-18 in the third period before winning the final quarter 25-17.
The other game in Group B on opening day saw Poland edge out Finland 67-65. Britain will face the Finns on Saturday before wrapping up the first round stage against the Poles on Monday. Realistically they will need to win both games to progress to the quarter-finals.
