The big striker converted a Danny Armstrong pass in the 59th minute of a pulsating last-16 tie in which the home side were well-organised and disciplined.

Killie withstood Celtic’s relentless pressure thereafter to complete a remarkable early-season Old Firm double, having beaten Rangers 1-0 on the opening day of the cinch Premiership.

The 1-0 defeat was a bitter and unexpected blow to the treble winners who have won the trophy six times in the previous seven seasons.

Kilmarnock boss Derek McInnes has certainly got his side off to a flying start this season.

After taking four points from six in their opening two Premiership fixtures, Killie were unchanged and confident.

With Cameron Carter-Vickers and Stephen Welsh injured, Brendan Rodgers gave a debut to 23-year-old Sweden defender Gustaf Lagerbielke while there was also a first start for summer signing Odin Thiago Holm.

Lagerbielke conceded an early corner when goalkeeper Joe Hart failed to collect his pass back and Killie defender Corrie Ndaba flicked a Danny Armstrong delivery just over the bar.

Second later at the other end, Hoops striker Kyogo Furuhashi stretched to knock a Holm cross past the post before midfielder Matt O’Riley’s tame shot from inside the box, after a terrific set-up by Furuhashi, was gathered by Kilmarnock keeper Will Dennis.

The ball continued to speed from end to end.

Celtic missed a chance in the 29th minute when Armstrong was robbed by Furuhashi near the touchline and the Japan international raced clear only to see his low drive blocked by Dennis.

Killie had an opportunity in the one minute of added time but Ndaba missed the target with a header from Stuart Findlay’s cross.

Celtic looked more purposeful and pacey at the start of the second half but in the 54th minute it was Hart who had to make a terrific save from Kyle Magennis’ drive from 16 yards.

However, when Celtic defender Greg Taylor was off the pitch getting treatment on a face knock, Killie took the lead.

Strong-running Watkins picked out Armstrong with a pass at the edge of the Celtic box and when he made space to send the ball back across the penalty area, the Killie striker had followed in to knock home from a few yards out.

Rodgers soon replaced Holm and Liel Abada with David Turnbull and Yang Hyun-jun and the travelling Hoops fans urged them forward.

Kilmarnock remained dogged and determined as they became penned into their own half.

Watkins made way for Kyle Vassell with Celtic’s Sead Haksabanovic on for O’Riley.

It was mostly backs-to-the-wall defending for the home side with midfielder Brad Lyons throwing himself in front of Yang’s shot to take the ball over the bar for another corner which Killie defended.

And after seven minutes of added time, they had held on for a stunning victory.