Goals from Mark Bentley and Wayne Gray saw the Shrimpers to a comfortable win against the Pirates, who they defeated in the LDV Vans Trophy as well.
Blues midfielder Bentley's rising shot forced a good save out of Bristol keepter Ryan Clarke before he opened the scoring on 14 minutes when the custodian spilled a Wayne Gray shot.
Gray made it two from the penalty spot on 26 minutes after being brought down by Rovers defender Craig Hinton.
Southend were in cruise control by now and saw a fine Clarke save deny a 20-goal top scorer Freddy Eastwood before Gray's header hit the crossbar.
Bristol rarely troubled Darryl Flahavan, with 20-goal leading striker Juniur Agogo's header being their only effort on target of the first 45 minutes.
Southend continuted to have the upper hand in the second half despite stepping off the gas.
Mark Gower skied a shot over on 46 minutes and two minutes later Clarke, who had a spell on loan with Southend this season, denied Gray with a great reaction save.
Bristol swtiched to 4-4-2 formation before half-time and the introduction of midfielder Ryan Williams added zest to the visitors' play.
But Ian Atkins' men still had trouble breaking down a defence that has only conceded three goals at home since Christmass.
Agogo's attempt to chip Flahavan was chested down by the keeper, skipper James Hunt's low shot was easily gathered and WIlliams' 12-yard effort on 90 minutes went wide.
The Shrimpers' previous record of 16 games without defeat was set in 1932 and it was 60 years later that Southend last topped the table, when a 4-0 win over Newcastle United saw them at the summit of old Division Two.