Bent, who scored 25 goals last season, took his tally for the new campaign to three in as many games, although he will rarely be presented with more gilt-edged chances as those which came his way tonight.
Cousins' misjudgment handed the former Tottenham frontman the opening goal with 20 minutes gone, and a handling error 17 minutes later gifted him his second.
The errors proved costly for the League One side, who forced home keeper Simon Mignolet into a series of fine saves either side of half-time.
However, Sunderland were worthy winners on a night when they never really had to find top gear to claim their first win of the season in front of a crowd of just 13,532 at the Stadium of Light.
Steve Bruce sent his players out desperate for them to get their season up and running after seeing them surrender a 2-0 lead at home to Birmingham to take only a point on the opening day of the league campaign, and then return from West Brom at the weekend empty-handed.
He made six changes, including the returns of skipper Lee Cattermole and Michael Turner from suspension, but his desire to ensure there were no slip-ups was reflected in his decision to field Bent, who might otherwise have been given an evening off.
In the event, the £10million man effectively had the game won by half-time and he barely had to break sweat to do so as Cousins endured a nightmare visit to the Stadium of Light.
Despite the strength of the side with which they started, the Black Cats had created little of note - Bent had headed an eighth-minute Bolo Zenden cross on to the roof of the net - until Cousins suffered his first rush of blood with 20 minutes gone.
Zenden's long ball down the middle looked harmless enough until the keeper inexplicably decided, wrongly as it transpired, that he could beat Bent to it, and the striker calmly headed it over him and into the gaping net.
Sunderland instantly looked a more cohesive unit and started to pass the ball with a fluency which had previously been lacking to pin the visitors back.
However, Cousins was the culprit once again eight minutes before the break as the same combination paid dividends for the home side.
He looked favourite to claim Zenden's inswinging free-kick, but under little pressure, he failed to hang on and spilled the ball at the feet of the astonished Bent, who needed no second invitation with the goal once again at his mercy.
Anthony Wordsworth almost dragged the visitors back into it with a 43rd-minute header which Mignolet turned on to the bar at full stretch, but Bruce's men headed for the dressing room knowing the game was all but won.
The wisdom of that decision was perhaps illustrated within the opening 12 minutes of the second half as Colchester made a genuine bid to get back into the game.
Mignolet had to made a solid stop from striker Kayode Odejayi's header, but he was extended much further to keep out midfielder David Perkins' curling left-foot shot.
The Premier League side failed to heed the warning and were fortunate to escape when striker Ian Henderson could not hit the target with a diving header from Brian Wilson's 55th-minute cross, and Mignolet had to beat away another well-struck effort from Perkins two minutes later.
It was a measure of Perkins' influence on the game that he received warm applause from the home fans when he was replaced by Ashley Vincent with 24 minutes remaining.
Substitute Martyn Waghorn was unfortunate not to cement Sunderland's victory with 15 minutes remaining when his long-range effort beat Cousins, but rattled the crossbar.
But Bent might have ended his night in style three minutes later when Richardson broke down the left and tried to pick him out in front of goal, only to deliver his low cross straight into Cousins' arms.