The result saw last year's treble winners fall even further behind Celtic in a championship race that has already seen bookies pay up on the Hoops, who moved 16 points clear by hammering Livingston.
The hundreds of Rangers fans whose journey to Dundee was delayed by a road closure must have wished they were back in a traffic jam when Kerr and McLaren hammered two more nails into their coffin with goals in a three-minute spell.
Rangers had created early chances with the recalled Michael Mols heading over and Mikel Arteta denied by a triple combination of a deflection off a defender, goalkeeper Paul Gallacher's outstretched hand and an upright.
But United's reply was to net twice in three minutes and Kerr's opener was a stunner, a drive from the edge of the area that bounced over the line off the crossbar.
That was a shock for the Rangers defence but worse was to follow as they allowed Barry Robson's corner to find McLaren at the back post for the ex-Scotland cap to bundle the ball home from close range.
Emerson scuffed a shot wide and Frank de Boer saw a free-kick deflected away off Chris Innes as Rangers sought a route back into the match.
It could have been much worse for the fallen champions had not McLaren's shot on the turn not taken such a deflection off Frank de Boer. That took it over Stefan Klos but also high enough to bounce to safety off the crossbar.
Gers boss Alex McLeish made two changes at the break with Arteta and Emerson replaced by Steven Thompson and Maurice Ross.
A third and final change followed 12 minutes later when Gavin Rae was able to make only his second appearance for Rangers since his transfer-window switch from Dundee, with Christian Nerlinger making way.
The changes turned out to be cosmetic as few chances of note were created by either side in the second period.
Craig Moore became an additional worry when he was hurt bailing out Ricksen.
The Australian hobbled back on after treatment for a leg injury, with Michael Ball having been booked in the 79th minute for upending Robson.
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