Paartalu opened the scoring in the 13th minute with a neat header from Thomas Broich's curling free-kick before Albanian striker Berisha scored his second goal in as many matches on the hour-mark following a pass from substitute Massimo Murdocca. Nichols wrapped up proceedings with just over 10 minutes remaining when Berisha played him to slot past United keeper Glen Moss.
The win has the Roar on top of the table on nine points and it extended their unbeaten streak to 31 matches.
Elsewhere in the A-League, Sydney FC recorded their first victory of the new season with a 2-1 come-from-behind result over Adelaide United at Hindmarsh Stadium. Dario Vidosic put the Reds ahead just before the half-hour mark before Jamie Coyne fired home and then Nick Carle completed the comeback with nine minutes remaining.
In the much-anticipated Melbourne derby on Saturday night, the Victory and Heart were locked in a scoreless draw in front of close to 40,000 fans as Harry Kewell and co. notched up a third game without a goal as the Newcastle Jets grabbed a second win of the campaign courtesy of Jeremy Brockie's brilliant solo effort in the 25th minute against Central Coast Mariners at Ausgrid Stadium.
2011/12 A-League season scores - Week 3
Melbourne Victory: 0 Melbourne Heart: 0 Etihad Stadium, Melbourne - 39,309