Central defender Turner thundered home a stunning and ferocious 20-yard shot in the 69th minute at Griffin Park to net his first goal of the season and hand Brentford three points.
It was a glorious way to win a hard-fought match in which Brentford battled hard to break down Tranmere's solid defence.
Rovers, in contrast, didn't manage a single shot on target all match and their early time-wasting came back to haunt them as Brentford clinched victory.
The result was also greeted with cheers at Kenilworth Road because it meant Luton were promoted and Tranmere could no longer catch them.
Bees boss Allen said: "It's a very good three points and what a goal! That boy has done great since he's been here.
"He's never anything outstanding and he doesn't win man-of-the-match because you don't notice him. But he just keeps playing the same consistent way.
"He has been practising his shooting, too. We've been telling him that in successful teams centre-backs have to score goals and he's been getting a bit of stick. So for him to score that was great. I was pleased it was the only goal as well because it had his name on it and he deserved it."
Brentford worked hard in a scrappy first half that was short on chances but they just about edged it.
Isaiah Rankin missed one opportunity from a Scott Fitzgerald cross and Turner, signed from Charlton this season, blasted a volley wide, while Darren Pratley had an effort saved.
But after the break the Bees stepped up a gear and deservedly went ahead when Turner got it right second time around.
He thundered home an unstoppable shot from the edge of the area after a left-wing cross had been cleared.
In a bruising encounter Brentford held on after that, also going close when a Rankin header was saved. But things got worse for Tranmere as defender Ryan Taylor was carried off with what looked a serious injury.
Rovers manager Brian Little said: "I thought we did well enough. But they scored a fantastic goal and there was nothing we could do about that. That strike was the only difference between the sides."