Match ends, Kilmarnock 2, Rangers 1.
Jordan Jones scored the winner against the club he will join this summer, as Kilmarnock came from behind to beat Rangers and move into second place in the Scottish Premiership.
The Northern Irish winger lashed in from 22 yards and ran to celebrate with manager Steve Clarke as the Ibrox side slipped three points behind Celtic.
Jermain Defoe scored 12 minutes into his Rangers debut but Eammon Brophy cancelled out the former England striker's close-range effort, robbing Joe Worrall before finishing sharply.
Rangers' top scorer Alfredo Morelos struck a post and had an effort ruled out after he punched the ball into the net as Steven Gerrard's side slipped to their fourth defeat of the league campaign.
The Ibrox side now sit third in the table, level on points with Aberdeen.
Resilient Kilmarnock punish vulnerable Rangers
Defoe did what Defoe has done throughout his career and he did it quickly, his debut goal coming after a dozen minutes at the tail-end of a siege on the Kilmarnock goal.
Goalkeeper Daniel Bachmann was a busy boy in that mad flurry, first tipping away a low shot from Andy Halliday, then diving at the feet of the in-rushing James Tavernier to stop the second wave. As the home defence remained comatose, the loose ball broke to Ryan Kent, and his effort was kept out by a clearance that only served to set up Defoe.
Again the Kilmarnock defence slept - and this time it cost them. Defoe had the easiest job, flicking it home from a few yards. Another one for the goals mountain the Englishman has constructed over the years - and pretty much the last impact he had on the evening.
In playing both of his new, and expensive recruits, Gerrard had to leave out two men who performed heroically for him in their last outing in the league - the 1-0 win over Celtic in December. Ross McCrorie, a rock in midfield that day, and Daniel Candeias, a bit of a dervish out wide, were sacrificed as the manager went with two strikers.
That early goal, and the one they nearly scored soon after when Morelos hit a post with a header, suggested that this was going to be a pleasing evening for the Rangers manager instead of another troubling one, of many, on the road.
Rangers had dropped points in six of their 10 Premiership away games this season and that vulnerability opened up again midway through the first half just when you thought they had the game under control.
It was a colossal error from the nervy Worrall that brought the equaliser. In possession just outside his penalty area, the centre-half switched-off to the danger around him. He was mugged by Brophy, who ran away from him, then steadied himself before shooting cooly past Allan McGregor.
We didn't need any more evidence of Kilmarnock's resilience under Clarke, but here was another example for any remaining non-believers - if there are any non-believers at this stage. Doubtful, it has to be said.
Just after the hour, the Ayrshire side hit the front. Rangers gave it away on the right and Jones, who had shipped such stick for the tweet announcing his pre-contract deal with Rangers, gobbled it up and moved downfield. Rangers backed off him. He had Greg Taylor outside him and for a second it looked like he was about to use him. He didn't.
Jones chanced his luck and his luck was in. His shot beat McGregor low to his right, the goalkeeper not exactly covering himself in glory in his slack attempt to keep it out. Cue mayhem at Rugby Park. What a moment for Jones. He was a busy and alert all night.
Kilmarnock then had to weather a storm. Alan Power had been their rock and his work-rate and leadership only grew when the hosts were forced to defend their lead. Stuart Findlay, too. This is a team of big men.
Worrall, Morelos and Kyle Lafferty - on for Defoe - had efforts on target but they could not beat Bachmann. Late on, Gary Dicker, another major force for the home team, cleared just as Morelos was lurking.
Clarke's men hung on - and they deserved to. A huge victory for Kilmarnock in a wondrous season. A massive blow for Rangers just after their January splurge in a bid to kick on for a title challenge that looks a lot more distant now.
'Rangers hobbled by defending' - analysis
Former Rangers striker Billy Dodds on Sportsound
Rangers were so dominant in the first 22 minutes but the circumstances of losing the goal shocked them. A few of the players were like 'wow, what just happened?'. But then Kilmarnock gained momentum - digging in, getting around the pitch, then getting the second goal and clinging on. It was all hands to the pump, bodies on the line.
A lot of managers would have panicked and changed their shape and tried to match Rangers up. But Steve Clarke didn't. He just believed in his squad. That's where Kilmarnock are as a squad just now.
'I know what Jordan is like' - reaction
Kilmarnock manager Steve Clarke: "I know what Jordan is like. I know he is committed to Kilmarnock until the end of this season. Jordan has got himself a fantastic move but that's for next season.
"We defended well when we had to. We put in a good shift and showed a little bit of quality in the finishes as well."
Rangers manager Steven Gerrard: "I think we created enough to win the game. Kilmarnock haven't put any combinations together or cut us open or looked like a team that were worrying us really.
"But you can't win football matches if you give silly gifts away. A square ball in the second half, on this type of pitch is something we asked the players to avoid at all costs."
- 26BachmannBooked at 12mins
- 27TshibolaBooked at 70mins
- 8DickerBooked at 88mins
- 6PowerBooked at 90mins
- 25BrophyBooked at 73minsSubstituted forBroadfootat 89'minutes
- 11JonesSubstituted forNdjoliat 90'minutes
- 36McAuleyBooked at 33mins
- 10DavisSubstituted forCandeiasat 70'minutes
- 9DefoeSubstituted forLaffertyat 79'minutes
- 20MorelosBooked at 50mins
- Don Robertson
- Shots on Target
Second Half ends, Kilmarnock 2, Rangers 1.
Attempt blocked. Scott Arfield (Rangers) left footed shot from the centre of the box is blocked.
Corner, Rangers. Conceded by Gary Dicker.
Alan Power (Kilmarnock) is shown the yellow card for a bad foul.
James Tavernier (Rangers) wins a free kick in the defensive half.
Foul by Alan Power (Kilmarnock).
Substitution, Kilmarnock. Mikael Ndjoli replaces Jordan Jones.
Attempt saved. Kyle Lafferty (Rangers) right footed shot from the centre of the box is saved in the centre of the goal.
Substitution, Kilmarnock. Kirk Broadfoot replaces Eamonn Brophy.
Gary Dicker (Kilmarnock) is shown the yellow card for a bad foul.
Ryan Jack (Rangers) wins a free kick in the attacking half.
Foul by Gary Dicker (Kilmarnock).
Gary Dicker (Kilmarnock) wins a free kick in the attacking half.
Foul by Kyle Lafferty (Rangers).
Ryan Kent (Rangers) wins a free kick in the attacking half.
Foul by Alan Power (Kilmarnock).
Corner, Kilmarnock. Conceded by Gareth McAuley.
Attempt blocked. Eamonn Brophy (Kilmarnock) left footed shot from outside the box is blocked.
Foul by Scott Arfield (Rangers).