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Rangers trailed at the break, through ex-Ibrox striker Kris Boyd's shot but recovered in the second half with James Tavernier's free-kick to draw 1-1.
"It's the worst display in the last 14 or 15 months," said manager Warburton.
"We move quickly and with quality on the training field and we didn't do that. We chose to go long and I don't know why."
Warburton's side, who won last season's Championship, have yet to keep a clean sheet in the Scottish Premiership this term, posting two 1-1 draws and two 2-1 wins.
"We draw with Hamilton in the first game and the end of the world is nigh," said Warburton of the expectations on his side.
"There is no shortage of desire and commitment. What we have to do is take it from the training pitch on to the match pitch.
"We have had passages of good play, Dundee second half and today second half. But we have to be better for longer.
"We have to play with a bit more belief. We looked hesitant at times in terms of our decision-making. That is very unlike us and we didn't get the ball moving.
"We have new players coming and there is maybe some gelling still going on."
Killie's Greg Taylor was dismissed for a second-half tackle on Joey Barton and Warburton said: "Joey is okay.
"I saw the challenge. We don't want to see anyone sent off, but it was a poor challenge.
"I was conscious the atmosphere was rising. He was on a yellow card, so I took him off as a precaution."
Meanwhile, striker Joe Dodoo was sent for an x-ray on his ankle after landing awkwardly early on.
Mark Warburton lamented his team's first-half display at Kilmarnock, saying: "It was not a Rangers team."