For the home side, whose supporters gave their visitors a raucous welcome, it was a deserved if somewhat nervous 1-0 victory that kept them in an automatic promotion spot.
Chesterfield, with games in hand over their rivals, still have a theoretical chance of making the play-offs themselves, but by not playing nine of the side that had done so well against Middlesbrough, Duncan showed where his priorities lie. "It was an outside chance, it's more outside now," the Chesterfield manager said of his promotion hopes afterwards.
Asaba's 23rd-minute winner was out of keeping with a game desperately short of skill or flair. It came after Chesterfield failed to clear Marcus Bent's cross from the right and the ball fell to Asaba who drilled it confidently home from 12 yards.
It needed that sort of finish to beat Billy Mercer, who along with Mark Williams was the only Chesterfield player to retain his place in the starting line-up. Mercer was impressive throughout but the goal invigorated the home side after a somnolent start and they produced their best football of the night in the period before half-time.
Robert Taylor could have doubled the advantage but after exchanging passes with Asaba his fierce shot went over the bar. Brentford created a couple of reasonable chances soon after the break but the longer the lead stayed at a single goal the more jittery they became. Notably when David McGhee's fluffed clearance allowed Tony Lormor a sight of goal. Fortunately for McGhee the resulting shot was well off target.
In the closing stages Duncan bought on Jamie Hewitt,whose goal had produced such a memorable finale to Sunday's game. Hewitt was unable to repeat the feat, but had he done so it would have been lost on David Webb. The Brentford manager confessed afterwards that he had not watched Chesterfield's semi-final. "I was doing my garden," he said.
Brentford (4-4-2): Dearden; Statham, Ashby, Bates (Omigie, 67), Anderson; Bent (Hurdle, 84), McGhee, Smith, Dennis; Asaba, Taylor. Substitute not used: Fernandes (gk).
Chesterfield (4-4-2): Mercer; Mitchell (Allison, h-t), Williams, Carr, Rogers; Dunn, Beaumont, Ebdon, Lund (Hewitt, 76); Mason, Lormor. Substitute not used: Lomas.
Referee: M Pierce (Portsmouth).
More reports, results, page 31