Sexton rang the changes, even though he had seen his youngsters open their campaign in the tournament with a 1-0 victory over Belgium on Friday courtesy of a Steve Slade goal.
And on Tuesday night, England paid the price as an early penalty by Caesar Muhonga - awarded when the Queen's Park Rangers player Chris Plummer fouled Sidonio Malamba - and a late strike by Valdo Costa gave Angola an unexpected 2-0 success.
"It was a disappointing result and a disappointing performance," Sexton said afterwards. "It's always a risk changing a team when you have a winning start.
"You would normally keep the same team but the usefulness of this tournament is to look at players. We started quite brightly but got caught playing square balls and balls back."
Manchester City's Michael Brown attempted to inject some life into England with two long-range efforts and Tottenham starlet Slade, who has already caught the future England manager Glenn Hoddle's attention, should have done better than blast a volley high and wide before the break.
But the writing was on the wall for Sexton's boys when Manchester United's David Beckham saw an effort hit the post, and Costa's breakaway effort sealed the issue.
"It's a learning question of what to do and what not to do," Sexton reflected. "I thought we deserved a goal and you would have put money on David Beckham putting his chance away.
"Their first goal was a silly goal to give away. We lost a bit of confidence and it's a knock to the lads' pride because they are better than that.
"But now nobody in football is surprised at the improvement in football throughout the world.
"Each country brings an important trait to the game. Everybody brings something to the game and nobody has got everything. It's good experience for the lads and to learn something for next time out."Reuse content