Sands had already been booked for a foul on Jordy Hiwula when he appeared to grab the Staggies striker to prevent him getting a clear run on goal.
Robertson took no action and the Light Blues subsequently went ahead in the 24th minute through a deflected shot from midfielder John Lundstram before in-form striker Antonio Colak volleyed in a second in 39 minutes.
Sands was replaced by Leon King for the start of the second half and Colak added a third just before the hour mark for his seventh goal in seven games.
Substitute Steven Davis knocked in a fourth with 10 minutes remaining to go one point ahead of Celtic at the top of the cinch Premiership, albeit the Hoops play at Dundee United on Sunday.
Mackay, who had Jack Baldwin and Ross Callachan suspended after being handed retrospective red cards for tackles in last week’s game against Kilmarnock, was bewildered by Robertson’s lack of action.
He said: “Sands pulls down Jordy with two hands around his waist.
“He’s already been booked but it’s inexplicable how it’s not a straight red, never mind a booking which would take him off as well.
“Rangers took him off at half-time which shows what they think.
“I can’t see how anyone who sees it on TV will think other than it’s a straight red. The dynamics of the game changes if he goes off.
“I’m not saying what it would end up but Aberdeen against Livingston was 0-0, Livingston lose a player after 40 minutes and it’s 5-0 to Aberdeen.
“The dynamics of games change and it certainly changed on that.
“There weren’t bodies in between, it was very straightforward.
“There was no need for him to go down, he rolled him and he was away.
“We are disappointed with that. It makes it even more sore that we’ve had two players cited and banned retrospectively by the Scottish FA during the week.
“Two of my best players aren’t here then something goes against you like that. It was clear as day. You need correct decisions to go for you at Ibrox.”
Asked if he had spoken to Robertson after the game, Mackay said: “At the end of the game I am pretty sure Don realises something isn’t quite right because he said if he got it wrong he’d call me tonight.
“The fourth official said he didn’t see enough. It’s one of those things.
“VAR will hopefully clear all this up but it doesn’t make it any better today.”
Rangers boss Giovanni van Bronckhorst admits Rangers were lucky not to go down to 10 men.
He told Sky Sports: “He was already on a yellow and it was one of those fouls that could go either way so for us it was lucky that he didn’t get the second yellow.
“Sometimes you are lucky with cards and sometimes it doesn’t go your way.”
Rangers qualified for the Champions League by beating PSV Eindhoven on Wednesday night and van Bronckhorst was pleased with the way his side remained driven for domestic duties.
He added: “It was a great result on Wednesday. We were on a high and very positive because we’re going to be playing in the Champions League.
“But we had to switch back to the domestic league and it’s always about the start and keeping the same standards you want and way of playing every game.
“The games are coming fast but when you start games like this you will never drop your levels of intensity and passing and movement.
“We reached a really high level. I was really pleased with the performance and clean sheet and the goals we scored were a really high level so I’m very pleased.”