The home side had only registered one win in their ten games this season, including consecutive defeats in their last five games
Millwall skipper Paul Robinson called on the team to pull together under the caretaker-manager in his programme notes and it was the home side who started the brighter.
And Robinson, who joined the club as a schoolboy, was determined to lead from the front and almost opened the scoring after just ten minutes when his header was hooked off the line.
Donachie's side continued to pile on the pressure but it was Brentford who broke the deadlock with a classic sucker punch.
Poul Hubertz headed just wide of the post and within a minute Brentford had taken the lead.
In a sweeping counter attack Jo Kuffour swung in a testing ball from the left which Calum Willock guided into the far corner.
The goal clearly rattled Millwall and they were almost two down minutes later when Lenny Pidgeley managed to tip right-back Karleigh Osborne's free header around the post.
To their credit Millwall fought their way back into the game and were back on level terms on 27 minutes when the impressive Danny Haynes, on loan from Ipswich an making his debut, skinned Osborne yet again before picking out Hubertz in the box.
Brentford keeper Stuart Nelson managed to parry the header from the big Dane, but Alan Dunne was on hand to smack the ball into the back of the net.
As the game got more heated the home side pressed and were unlucky not to take the lead before half-time when Haynes headed against the crossbar with Nelson well beaten and Dunne had his looping header cleared off the line by John Mousinho.
Brentford had penalty claims waved away either side of the break by referee Peter Walton who did well to keep a lid on a full-bloodied encounter hat threatened to boil over at any minute.
The home side missed a string of decent chances in the second half, but a defeat would have been harsh on the visitors who looked good value for a well deserved draw.