Jomel Warrican supported well with 2-28 from 10 overs and Brathwaite followed up a half-century for the visitors with 2-42 from seven overs.
The result gave the Sagicor HPC a 1-0 lead in the three-match series, which continues tomorrow at the same venue.
Brathwaite, the visitors’ captain, had led the way for his side with four fours and two sixes in 64 from 78 balls, as they were bowled out for 225 in 48.2 overs.
Kyle Hope made 44 and Jermaine Blackwood added 30, but the emerging West Indies players scored in fits and starts, as leg-spinner Marshall Ayub finished with 4-21 from five overs and teenager Taskin Ahmed 2-37 from 5.2 overs.
The Sagicor HPC team were then put under pressure, when Imrul and Anamul Haque batted with enterprise early against the new-ball pair of Jason Dawes and Dawnley Grant.
But Brathwaite triggered a top-order slide, when he removed Anamul caught close to the wicket for 12 and Shahriar Nafees caught behind for a duck in the space of three deliveries in his first over.
Dawes followed up, when Bangladesh-A captain Raqibul Hasan was caught behind for a duck next over, leaving the hosts 32 for three in the seventh over.
The Caribbean side met defiance, when Shamsur Rahman came to the crease and put on 89 for the fourth wicket with Imrul before he was caught behind for 38 off Warrican, giving wicketkeeper Jahmar Hamilton the last of his three victims behind the stumps.
Permaul delivered a major blow, when he removed Imrul four overs later, after the left-hander struck seven fours and two sixes in 61 from 83 balls.
But the Sagicor HPC ran into another roadblock, when Naeem and Marshall came together to put on 41 for the sixth wicket.
Four wickets – three to Permaul – for 12 runs in the space of the 39th and 43rd overs virtually handed the Sagicor HPC the match, although Naeem threatened with a vigorous rearguard action before Permaul ran him out in the penultimate over for 52 which contained just two fours from 67 balls.
Earlier, the Sagicor HPC team stumbled to 33 for two in the seventh over before opener Jermaine Blackwood and Hope stabilised the innings with a stand of 43 for the third wicket.
After Blackwood fell in the 14th over, the visitors failed to build a significant stand until Permaul joined Brathwaite and put on 51 for the seventh wicket before he was caught in the deep off left-arm spinner Enamul Haque Jr for 17 in the 42nd over, as the innings waned.
The Sagicor HPC players are on a month-long tour of Bangladesh.
SAGICOR HIGH PERFORMANCE CENTRE (maximum 50 overs)
A. Fletcher lbw b Ahmed 11
J. Blackwood c Ahmed b Apu 30
M. Barclay lbw b Hossain 7
K. Hope lbw b Ayub 44
K. Lesporis b Islam 12
C. Brathwaite c Ahmed b Ayub 64
J. Hamilton c Ahmed b Ayub 1
V. Permaul c Ahmed b Enamul Haque Jr 17
J. Dawes not out 10
J. Warrican lbw b Ayub 1
D. Grant b Ahmed 14
Extras: (b-1, lb-2, w-10, nb-1) 14
Total: (all out, 48.2 overs) 225
Fall of wickets: 1-26, 2-33, 3-76, 4-103, 5-134, 6-136, 7-187, 8-206, 9-208.
Bowling: Shahadat Hossain 8-0-43-1 (nb-1, w-1); Taskin Ahmed 5.2-0-37-2 (w-3); Enamul Haque Jr 10-0-40-1 (w-2); Nazmul Apu 10-0-52-1 (w-2); Naeem Islam 10-1-29-1 (w-2); Marshal Ayub 5-0-21-4..
BANGLADESH-A (target: 225 off 50 overs)
I. Kayes c Barclay b Permaul 61
A. Haque c Fletcher b Brathwaite 12
S. Nafees c wkp. Hamilton b Brathwaite 0
R. Hasan c Hamilton b Dawes 0
S. Rahman c wkp. Hamilton b Warrican 38
N. Islam run-out 52
M. Ayub c Dawes b Permaul 18
S. Hossain lbw b Permaul 1
T. Ahmed c Brathwaite b Warrican 0
E. Haque Jr lbw b Permaul 2
N. Apu not out 15
Extras: (b-1, lb-2, w-10, nb-2) 15
Total: (all out, 48.5 overs) 214
Fall of wickets: 1-31, 2-32, 3-32, 4-121, 5-127, 6-168, 7-175, 8-176, 9-180.
Bowling: Dawes 10-0-56-1 (w-1); Grant 4-0-25-0 (w-3, nb-1); Brathwaite 7-0-42-2 (nb-1, w-4); Permaul 10-0-29-4 (w-1); Blackwood 7.5-0-31-0; Warrican 10-2-28-2.