Basketbnall coach Alan Keane blasted his Feltham Warriors U18s side after they lost their unbeaten record against Guildford Heat last weekend.
Having beaten Guildford by 15 points earlier in the season, Warriors looked certain of victory with a 16-point cushion at half-time.
But Guildford got some baskets back and put the pressure on, leading to some stray passes from the Feltham side, and they lost the lead with three minutes remaining for a major upset, losing 95-87.
Keane said: "I was furious with the attitude and casual approach the players had towards the game, which they thought was won by half-time.
"Let's hope it's a valuable lesson learned for these young Warriors."
By contrast, coach Rudy Harriott was more than pleased with his U16 troops, despite going down to a second successive narrow defeat.
Last week, they went down 56-52 to league leaders Newham Youngbloods, despite several inside baskets from Baz Baban, others from Dalvin Nyark and Joe Pomilis, two excellent three-pointers from George Fletcher and sparkling approach play by Ben Ohene.
This time round, they pushed a very strong and unbeaten London Pioneers side all the way but came up just short 63-53.
Ohene again showed he is one of the best young players in London, while Fletcher and Joel Joseph led the charge with some excellent three-pointers.
Pompilis and Baban battled well against much taller Pioneers players, while Shakir Rahim picked off passes with ease.
Rahim, with some tough defence, and Joseph, with some well-taken baskets also starred for Davit Cherkezishvil's U15s, as they beat Herts 70-57 at Feltham Community College.
Rahim's Lampton School mate and new signing Haki Nsugba had an outstanding debut, with his presence and rebounding ability triggering a lot of fast break points.
Nyark, who stands at 6ft 2ins, was a constant thorn in the Herts side, who found his height too much to deal with.
Alex Cadore and U14s prospect Nanad Djurdjevic also played well, while Joseph and Baban top-scored with 18 points each.
Andy Justice's U14s are top of their league with four games left after 29-18 win over Guildford Heat.
James Woodburn-Hall, Zabi Osmani, Prabseh Katawal and Jay Ramgi were all stars.
Also top of the table are Wes Francis' senior side, starring the likes of Arun Fernando, Nathanael Coley Prince, John MacCauley and U18s star Dominik Harriet.