GB women were beaten 55-40 by an experienced Belarus team on the opening day of their EuroBasket campaign in Poland.
Coach Tom Maher's team fell behind in the second quarter and slipped to an 18-point deficit in the third as Belarus turned the screw.
Kim Butler led GB's scorers with eight points and Azania Stewart added seven.
The team take on World Championship runners-up the Czech Republic on Sunday in their second game.
GB started confidently enough in a first quarter when neither side shot the ball well and Maher's team worked hard to offset Belarus's height advantage.
Trailing 11-14 fter the first 10 minutes, GB then scored only one backet in the first six-and-a-half minutes of the second quarter, during which their opponents established a 27-13 lead with more aggressive rebounding.
Baskets from Stewart, Butler and hard work from Julie Page before the interval meant GB trailed only 31-20 at the break, but they struggled again at the start of the second half.
Belarus opened with a spree of easy baskets on the break and led 40-25 when Tatsiana Likhtarovich hit a three-pointer with 5:24 remaining.
GB trailed 45-28 at the end of third quarter, having missed three-quarters of the 40 shots they had taken and without a success from three-point range, a shortcoming that has haunted them for much of the summer. It was a lead Belarus were never likely to to let slip in the last 10 minutes.
GB's star player Johannah Leedham hit four points in her 20 frustrating minutes on court and looked short of her usual sharpness.
Belarus were led by Anastasiya Verameyenka and Katsiaryna Snytsina, who scored 10 points each.
"We worked hard and that is the important thing," said Maher. "We've never played against sides of this level before - certainly not in official competition, so I'm happy with our performance."
"It was our first major finals game in Europe and we showed people that we can play at this level," said Page. "We talked before the game about playing tough defence, and I think we did that."
GB take on another strong contender, the Czech Republic, on Sunday evening in their next match.