However the powerful Croatians, who will take part in next month's Olympic qualifying tournament in Turkey, imposed themselves from the opening quarter as the visitors were given an immediate challenge on the road to London.
"We always knew it was going to be tough moving from the safe environment of training camp, where you can immediately correct mistakes, to a game where you have to get things right," said Maher.
"We have to accept that we'll need a few games to make the transition," he added.
Cheshire-born forward Jo Leedham had a team-high 15 points and added 6 rebounds for Great Britain, who trailed 35-23 at half-time.
Maher's side - with Chantelle Handy back in action after a foot injury - trimmed the deficit to 52-42 entering the fourth quarter but the hosts produced another surge to pull away.
Natalie Stafford added 13 points for GB.
The two sides meet again on Tuesday.