Danny Wilson's Blades have recorded back to back away victories over Yeovil Town (1-0) and Hartlepool United (2-1) and now Leyton Orient to extend there unbeaten run to thirteen league games and fly to third in the table behind Stevenage and first placed Tranmere Rovers - all of which have yet to lose a league game this season.
United were without skipper Neill Collins through injury, with Marcus Williams deputizing and with just over 10 minutes played-out the visitors lost keeper Mark Howard to injury with Academy keeper George Long taking to the field but was able to hold a clean sheet against the Londoners who had recorded just one defeat in six matches.
The Blades were on the attack from the start with defender Tony McMahon firing over on his unfavoured left foot and with eleven minutes gone Howard was forced to leave the game with a thigh strain, being strechered off and replaced by Long who was immediately protected by Matt Hill making a timed tackle on Cox.
McMahon was having a good game and fired wide once before before his cross was met by Blackman, but the former Blackburn Rovers striker shot over on 16 minutes. As the first half wore on opportunities dwindled but the home side went close through Smith and Chorley's header following a corner was kicked off the line by Dave Kitson.
Before the half-time whistle blew, midfielder Kevin McDonald fell and wasted a good opportunity after being fed by Ryan Flynn and Kitson, on the right fired his shot wide - there was also time for Paul Gallagher to hit a 25 yard effort wide of the mark.
In the second half the Blades once again started brightly and put in a good Brazilian move which involved 20 passes before the move ended in Flynn winning a corner - but on two occasions Blackman was penalized for handball.
Before the hour mark had passed United were rewarded for there efforts when a throwing was intercepted by United and Kitson found Blackman in space, he turned and fired a fierce rasping shot into the top corner from 20 yards out; 1-0.
Griffth hit wide in a move that involved Lisbie and Cook as the home side looked to add a response, but the Blades were soon on the attack and on 67 minutes almost doubled their lead - keeper Allsop denying Doyle with both feet as the captain changed after Flynn's ball through.
Long made an amazing save with 20 minutes remaining from Lisbie's header, unaware that the former Charltom striker was offside he kept him out and soon afterwards Cook fired a free-kick over.
Five minutes were added by the officials with the home side failing to muster an dangerous attack.