The opening goal came after six minutes as Emnes linked with Digard who swept a low cross to the far side, where Gary O'Neil scored past David McEwan.
Boro made it 2-0 in the 42nd minute when a Justin Hoyte cross from the right-hand edge of the box was inadvertently headed past his own keeper by Mick Dunlop, who was stretching to head clear.
Entering injury-time, Hoyte was fouled inside the penalty area by Ben Gordon and Aliadiere sent McEwan the wrong way from the spot.
Half-time: Dumbarton 0 Middlesbrough 3
With 70 minutes played Adam Johnson as he lashed the ball into the roof of the net from 20 yards.
Boro grabbed another three minutes later as Williams rose highest to a Josh Walker corner and his header beat a covering defender on the line to make it five without reply.
MIDDLESBROUGH: Jones (Coyne 46), Hoyte (McMahon 72), Bates (Wheater 72), Huth (Hines 72), Grounds (Taylor 72), O'Neil (J Johnson 72), Arca (Capt) (Williams 72), Digard (Walker 29), Yeates (A Johnson 65), Aliadiere (Franks 46), Emnes (Porritt 63).