Kayky's eagerly-anticipated Manchester City debut ended in defeat, as the young Blues collapsed to a heavy defeat in their final EFL Trophy group game at Rotherham.
City must now wait for the result of Scunthorpe and Doncaster's clash in a fortnight to discover whether they will progress to the knockout stages, but their fate is out of their hands after a disappointing evening in South Yorkshire.
This never felt like a 5-0 game, however, with City on top in the first half and with plenty of positives to take plus a club debut for summer signing Kayky, as well as a return from injury ahead of schedule for Liam Delap. Three goals in 14 second half minutes decided this tie, though - likely along with City's knockout hopes - as the League One side schooled their academy counterparts.
In City's last outing in this competition, Pep Guardiola took seven academy regulars for the first team Carabao Cup fixture with Wycombe on the same night. With the next round of that competition on Wednesday night, there was a danger that some of the academy's better players could be called up again, weakening them for this crucial decider at Rotherham.
But City went strong at the New York Stadium, with just Cole Palmer and Sam Edozie missing from the squad and presumably in contention for first-team involvement at West Ham. Still, that left the returning Delap, the free-scoring James McAtee, Romeo Lavia and Josh Wilson-Esbrand to start for a game City realistically needed to win to stand any good chance of progressing.
There was also an eye-catching inclusion on the bench, in summer recruit Kayky, included in a City matchday for the first time after a period of training with the first team.
Millers manager Paul Warne said in his programme notes of the young Blues that 'you're not at City at 18 if you're an egg.' And the youngsters soon endorsed that message, putting together some good moves in the opening stages. Delap and Micah Hamilton had half chances, while James McAtee was growing in influence and set up Delap to fire over.
Rotherham were the more physical of the two sides, but as joint-top goalscorers in this competition before this clash, they were showing their danger in attack as well, not giving City a second to put their foot on the ball. Still, as they often do, City were finding a way through the press either with intricate passing or direct running. Rotherham's only response was to stop them illegally, picking up three yellow cards in the first half alone.
City responded with some trickery and flashes, but couldn't create any clear-cut chances in an entertaining first half, Delap was unlucky not to be on the scoresheet as he came through 45 minutes unscathed on his return from injury.
But Delap was to make way at the break, likely a pre-planned move with summer signing Kayky on for his first appearance in a City shirt in his place. City paid an initial £9m for the Brazilian from Fluminese, and he has trained with the first team since his arrival at the club.
As all eyes were on the teenager, however, Rotherham took the lead, substitute Will Grigg deflecting a shot past the helpless Ciaran Slicker. Kayky could have equalised immediately after, but leant back and curled a good effort over after good work from McAtee.
That proved costly, as City would go 2-0 down through a penalty clumsily conceded by Finley Burns. Kieran Sadlier, who missed two good chances one-on-one moments before, made no mistake from the spot, and it was soon three as Jake Hull headed in from a corner.
It was a collapse that could end City's progress in the EFL Trophy this season. Defeat leaves them relying on the Football League's bottom club Scunthorpe to beat Doncaster in the final game, but not by more than a five-goal swing, and any positive result from Doncaster will see them progress at the expense of City.
There was little more City could have done, with a strong team fielded bar perhaps Palmer and Edozie. They had the chances, especially before the game-changing second goal, but failed to take them - and that will be a lesson for future outings in this competition or others they are involved in.
Rotherham are the competition's top scorers, and underlined their ruthlessness with a fourth with ten minutes remaining, Sadlier firing home his second. The forward completed his hat-trick on the stroke of 90 minutes, curling home a free kick from the edge of the area to put a rather unfair gloss on the scoreline.
It was a lesson for the youngsters of City, who had frustrated the hosts before the break with their technical ability, before learning a lesson themselves in the second half with a professional display of ruthless attacking by Rotherham.
As for Kayky, his introduction to English football couldn't have gone much worse - introduced at 0-0 before losing by five goals. He looked bright in sparks, drifting across the front three and creating space and a couple of half-decent scoring chances. That will be an encouragement for City, but EDS coach Brian Barry-Murphy may rue his miss at 1-0.
Now, City wait to see if they are given a lifeline in the Papa John's Trophy, but they can at least take the positives from Delap's bright return and Kayky's first outing in Blue.
