Aberdeen now face an almighty battle to retain their status as Scotland’s second force.
This damaging defeat cut second-placed Aberdeen’s lead over Rangers to just three points.
It also raised major concerns ahead of round two in the double header at Pittodrie on Sunday.
Outplayed and outfought by a managerless Gers for the opening 45 minutes in Govan, the Reds were shocking.
It was far better after the interval but by then the damage had been done.
Rebuilt in the summer, this Dons team has been like Jekyll and Hyde so far – capable of the good and the bad.
This, like the shocker against Motherwell only 11 days ago, was the bad and they cannot afford a repeat on Sunday.
Although second in the Premiership, the Dons have been comprehensively outplayed and beaten by Rangers, Celtic and Motherwell – twice.
One minute the Reds look like they have clicked and will surge to a run of wins – then they produce a performance like Ibrox.
An Aberdeen victory at the weekend will restore the six-point lead they held before slumping at Govan. Another defeat will allow Rangers to leap frog into second on goal difference.
It would be a colossal switch in fortunes and Sunday’s clash is now a must win for the Reds
Aberdeen cannot afford to be playing catch up in the league when Rangers’ long managerial saga finally ends.
What is clear is that whoever does get the Rangers gig will not inherit the shambles their back-to-back losses to bottom six sides Dundee and Hamilton had suggested.
They could have been vulnerable after those losses, yet it was the Gers who came out with the more intent.
There were multiple back-stories to the game with recent speculation making boss Derek McInnes favourite for the vacant Ibrox job.
McInnes brushed off any Rangers links last week by emphasising he was staying at Pittodrie. There was also the issue of former Dons skipper Ryan Jack coming up against his former team-mates.
All bubbling beneath the surface of a fixture with enough juice at best of times.
There was one change to the Aberdeen side that convincingly defeated Kilmarnock 3-1 at the weekend Kari Arnason returning, slotting into a back three.
Winger Gary Mackay-Steven dropped to the bench.
The back three didn’t work and was ditched towards the end of the first half – but the damage had been done with the Reds two goals down.
Rangers grabbed the opener in the sixth minute when Greg Tansey conceded a needless penalty after swiping at fresh air and connecting with Jason Holt.
James TAVERNIER stepped up to convert from the spot.
Arnason connected with a Tansey corner in the 22nd minute but his header flashed just wide.
It was 2-0 when Holt broke down the right and drilled a low cross into the box and Carlos PENA got in front of his marker to shoot across Lewis and home from eight yards to punish slack defending.
Joe Lewis saved from Tavernier at the near post in the 34th minute, then Stevie May shot into the side netting from close range.
Aberdeen had no width in attack and looked vulnerable on the flanks when Rangers were pushing forward.
In an attempt to rectify that McInnes took on Mackay-Steven for Tansey before half-time and switched to a back four.
Within a minute, GMS was in the heart of the action with a penalty claim when he was slightly clipped before shooting wide. The winger’s appeals for a spot kick were so vehement he was eventually booked.
On the hour mark Ryan Christie tried an audacious curling shot with the outside of his boot but Wes Foderingham saved the 20-yard effort.
Rangers went three ahead in the 71st minute when Windass held up the ball at the right edge of the box.
He then slid a pass wide of Considine to TAVERNIER, who drilled past Lewis from eight yards.
It went from bad to worse in the 84th minute when Christie was sent off for a second yellow for sliding in on Ross McCrorie from behind.
Both bookings were needless and costly as the attacker will now be suspended for Sunday.
It was the final blow in a dismal night for the Dons.
ABERDEEN: Lewis, Logan, Shinnie, Considine, O’Connor, McLean, Arnason, Tansey, McKenna, Christie, May.
SUBS: Mackay-Steven (for Tansey 43), Stewart (for Arnason 78), Roooney (for Mackay-Steven 83)
SUBS NOT USED: Reynolds, Maynard, Ball, Rogers.
RANGERS: Foderingham, Tavernier, John, Wilson, Jack, Miller, Windass, Alves, Holt, Pena, McRorie.
SUBS: Candeias (for Pena 68), Herrera (for Miller 83), Hardie (for Windass 89)
SUBS NOT USED: Alnwick, Hodson, Kranjcar, Bates.
REFEREE: Andrew Dallas.