Jordan Jones, who has been signed on a pre-contract deal by Gerrard, scored the winner for Killie as they hit back from falling behind to a debut goal for Rangers by Jermain Defoe.
It saw the Rugby Park side climb above Rangers into second place in the Premiership table, a point behind leaders Celtic. The champions, beaten 1-0 at Ibrox in the final game before the winter break, are now three points clear of third-placed Rangers with a game in hand.
Gerrard was left exasperated by the setback in which basic errors from Joe Worrall and Ryan Kent led to Kilmarnock’s goals.
“I think we have [undone the Old Firm win],” said Gerrard. “We got a lot of praise for beating Celtic. We won every single key individual battle in that game. But I’m struggling to find one of them tonight.
“So we deserve the criticism and have to suck the pain up over the coming days. It’s even more painful because we had so much control in the first 15 minutes of the game and looked so good.
“One moment had a huge effect on us and that’s a concern.
“It is a difficult one to take. Having started the game so well, having complete control and taking the lead, creating more dangerous opportunities to extend the lead.
“Then a huge mistake gave Kilmarnock the opportunity to get back into the game.
“That moment affected the whole team and the whole atmosphere in the ground. We never recovered at all from it.
“I know when I sit down and analyse the game later, it will be us having all the ball, us trying to create stuff. The two big moments which have gone against us, we have gifted Kilmarnock.
“There was Joe’s moment for the equaliser and then a square ball in the second half which sees us get done with a counter attack. We backed off Jordan and let him onto his favoured foot.
“A player of that ability is going to punish you from 20 yards. Him scoring the winner adds to the pain, but what can you do?”
Kilmarnock manager Steve Clarke praised the attitude of Jones who had been criticised by some of his club’s fans for his public expression of delight when his forthcoming move to Rangers was first announced.
“That tells you Jordan can handle big pressure and that’s a good thing for him going forward,” said Clarke.
“He’s been great for the club for two and a half seasons and I look forward to him being great for this club until the end of the season.”