Manchester City's Premier League title celebrations were delayed by a 2-1 defeat to Chelsea on Saturday in a rehearsal of this month's Champions League final.
Pep Guardiola's side are on the brink of a third championship in four seasons but could not complete the job at the Etihad Stadium after Sergio Aguero allowed Edouard Mendy to save a tame spot-kick.
That effort would have added a swift second to Raheem Sterling's breakthrough strike on the stroke of half-time.
Instead, Chelsea rallied after the interval and scored through Hakim Ziyech – their FA Cup semi-final hero against City – and then, in the final seconds, Marcos Alonso to boost their top-four aspirations and keep the leaders waiting, unable yet to turn their focus to the European showpiece.
Although Guardiola's puzzling 3-3-4 formation initially had Chelsea on the back foot, it was a defensive mishap rather than a tactical manoeuvre that forged the opening on 44 minutes.
Andreas Christensen misjudged a bouncing ball and was brushed aside by Gabriel Jesus, who squared for Aguero in front of an open goal, only for Sterling to sweep into the net when his team-mate dallied.
Aguero did not have to wait long for his next chance, as Christensen hobbled off and Jesus tangled with Billy Gilmour before Chelsea were able to introduce a substitute, prompting a City penalty.
However, as Thomas Tuchel fumed at the officials, a dreadful Panenka attempt from Aguero was gathered by Mendy.
The shortcomings of the City system were then laid bare shortly after the hour mark when Rodri – their sole central midfielder – lost out to Ziyech and left space for a Chelsea attack which ended with the same man arrowing a low finish beyond Ederson.
Chelsea pushed for a winner but were twice denied by the offside flag. Timo Werner had already strayed before netting in the first half and did so again, before a closer call kept substitute Callum Hudson-Odoi off the scoresheet.
City furiously appealed for a second penalty when Sterling went down under pressure from Kurt Zouma, but the final twist was in Chelsea's favour as Alonso's scuffed shot looped over Ederson.