Southend will justifiably feel the scoreline was harsh but for Sunderland the numbers do not lie.
Another three goals on home turf.
A third clean sheet in a week, and five wins on the bounce.
Peterborough United boss Steve Evans admitted earlier this week he was worried that the Sunderland 'juggernaut' was gathering pace and that certainly seems to be the case.
With a game in hand, they are now just three points behind Portsmouth in top spot.
They were not always at the best here but they scored three wonderful goals and created plenty more openings.
The hosts had started much the better of the two sides, and were almost ahead just moments after kick-off.
Reece James crossed from the left and Jerome Sinclair headed well, turning the ball across goal from the front post. Mark Oxley did well in the Southend goal to claw the ball away.
Lee Cattermole also went close when he drove a low effort from distance, the ball flashing wide of Oxley's goal.
The visitors began to find their feet and stretch the hosts, but their rhythm was understandably disrupted by a serious injury to left-back Ben Coker. Coker went down with no player in close proximity as he tried to turn. The screech of pain was piercing and the stretcher quickly called for.
A well-worked goal on the half-hour mark then saw the Black Cats take the lead.
Sinclair did well to spot a slack backpass to Oxley, pressing fiercely and forcing the goalkeeper to hack his clearance into a dangerous area. Cattermole collected and quickly switched the ball to the right flank, where Lynden Gooch delivered a good cross. George Honeyman delicately flicked the ball goalward and Oxley couldn't keep it out.
It should have been two when Gooch moved into space, Sinclair making an excellent run off the shoulder of the centre-back. Gooch took too long and the danger passed.
Sunderland then had to survive a tricky spell before the break.
Harry Bunn sent in a dangerous cross from the left, with a deflection off Jack Baldwin forcing a smart stop from Jon McLaughlin. The ball broke free and after one excellent block from Dylan McGeouch, Simon Cox fired over.
Cox then had a good chance to score from a corner, free at the back post after former Black Cat flicked the delivery on. His header, however, was weak and straight at McLaughlin.
The visitors started the second half brightly but it was a moment of individual brilliance that settled the game.
Another loose pass out from the back saw Chris Maguire pick the ball up 40 yards out. He advanced on goal and with the covering midfielder hovering over his shoulder, he unleashed a stunning effort that flew into the top corner.
Jack Ross shuffled his pack after Chris Powell's side responded strongly, and Sunderland were indebted to their goalkeeper for a superb block from Yearwood.
Southend were continuously threatening but inevitably left spaces in defence.
Substitute Aiden McGeady almost benefited, his excellent cross headed over by the diving Gooch.
McGeady was finding space on countless occasions wide on the left, and so it was unsurprising that it was the winger who added Sunderland's third. Substitute Josh Maja did superbly to play the pass, escaping the attentions of two defenders to free his team-mate. Oxley had no chance as the Irishman fired across goal.
From there it was a procession, the Black Cats starting to build serious momentum in their promotion push.
Sunderland XI: McLaughlin; Matthews, Flanagan, Baldwin, James; McGeouch (McGeady, 54), Cattermole, Honeyman; Maguire, Gooch (O'Nien, 74) , Sinclair (Maja, 58)
Subs: Ruiter, Oviedo, Ozturk, Mumba
Southend United XI: Oxley; Demetriou, Turner, Moore, Coker (Hendrie, 21); McLaughlin (McCoulsky, 66), Manton, Dieng, Bunn; Yearwood (Kightly, 78), Cox
Subs: Bwomono, Bishop, Robinson, White
Attendance: 30,894 (1,130 away)
Bookings: Bunn, 41 Flanagan, 45 Yearwood, 68