BEES boss Thomas Frank felt his side gave a good account of themselves but rued the errors that led to both goals.
Brentford’s loss was their fifth in succession as their recent slump, after a bright opening to the campaign, continues.
Mahrez scored for Manchester City after dominating the first half with a 40th-minute penalty before De Bruyne sealed the 2-0 win at the Etihad Stadium after a David Raya error in the second half.
“From a defensive perspective we were almost perfect,” Frank said. “But the two goals – the penalty we should never give sway, don’t slide down in the penalty area, and the second goal was a bad mistake.
“We made it difficult for them. The structure, discipline and mentality were there but those decisive moments, we didn’t take them, and we got punished at the other end.
“We made those mistakes but the overall performance will give us confidence.”
The loss was the Bees’ fifth in succession in the Premier League but Frank is backing his players to reverse the slump.
He said: “It is very important we look at the work ethic and the attitude – a top attitude – and performances have been really good.
“We have to keep the performance and the mentality and stay positive, then we will be fine.”
Striker Ivan Toney missed the game with a calf injury but could return for Saturday’s clash with Crystal Palace.
“I hope so, fingers crossed,” said Frank. “We will assess him every day.”
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