By Rob Dugdale
BBC Sport in Skopje
GB's Deng (left) gets quickly closed down by Macedonia's players
Great Britain lost for the first time this summer as they were convincingly beaten 75-56 by Macedonia in Skopje in their European qualifying campaign.
GB were sluggish from the outset and trailed by as many as 29 points before a late run salvaged some pride.
Meanwhile, the GB women's team continued their impressive run with a 70-63 win over Slovakia in Kosice.
Both teams are certain to qualify for next year's EuroBasket finals, though, if they win in Liverpool on Thursday.
As well as losing for the first time in Group B, GB's men have also slipped behind in the tie-break procedure against Macedonia, a team they beat 104-96 in overtime in Newcastle two weeks ago.
three qualifying groups in action this month
, with the group winners and the best two second-placed teams going through to next year's EuroBasket finals in Lithuania.
Pops Mensah-Bonsu hit 17 points for GB's men and Luol Deng added 14 but it was to no avail.
GB coach Chris Finch said: "It was a match that we felt was coming.
"I didn't think were ready to play at the level we needed to play at and it showed."
Off the ball, they're holding a grabbing him all the time - he's not getting the respect he deserves
GB coach Chris Finch on Luol Deng
Spurred on by a partisan 8,000 crowd, Macedonia took the first quarter 22-14 and hit eight three-pointers in the first half, a figure that contrasted sharply with GB's one success from eight attempts from the free throw line.
Despite good cameo performance off the bench from Kieron Achara and Matthew Bryan-Amaning, GB trailed 43-27 at half-time and were 20 points down by the end of the third quarter.
Macedonia, led by 20 points from naturalised American player Bo McCalebb, piled on the agony in the final period, leading 69-40 before a late flurry of points from Deng brought a faint semblance of respectability to the score.
But Finch hit out at what he felt was a lack of protection for his star player from the officials.
"I don't think it's fatigue with Luol," said Finch. "It's disgusting to watch what's happening out there - it's hard to find who the NBA player is.
"Off the ball, they're holding a grabbing him all the time - he's not getting the respect he deserves. He's creating and driving hard, but he's frustrated because he's not getting the whistle that he deserves."
Finch compared the indifference of officials with the more favourable approach shown to other NBA player Tony Parker of France and Spain's Pau Gasol in last year's EuroBasket finals.
Finch admitted that the GB offence has floundered recently, producing just 122 points in the last two outings.
"We've got to play better next game," he said. "We've got to get Luol and Pops back on track."
Mensah-Bonsu admitted: "Like the coach said, we kind of saw this one coming. We just have to put this one behind us and move on."
hit six three-pointers in her 26 points and Natalie Stafford added 10 points as GB stormed back after losing the first quarter by 10 points to go top of Group D.
Coach Tom Maher said: "Jo Leedham was sensational but it really was a team effort. We're pretty sure this is Britain's first win over Slovakia, so we are all pretty proud."
The win means that the women can qualify for the EuroBasket finals if they beat Germany in Liverpool on Thursday.
The men face Bosnia at Liverpool's Echo Arena later the same evening, knowing a win is certain to take them through with a game remaining.