John Terry's own goal took the title out of Chelsea's hands, and prompted Palace's best-ever Premier League run as they won their next four games to secure what had previously appeared an unlikely survival.
Meanwhile, the Blues fell away and missed out on the championship, but they are a different animal this season and visit Selhurst Park five points clear at the top of the table following an unbeaten start.
Costa, who opened his international account for Spain in the week, is four clear at the top of the Premier League scoring charts with nine in seven games since joining in a £32m deal from Atletico Madrid.
The contribution of Fabregas in his blistering start to English football cannot be overlooked, with the midfielder the leading assister in Europe, although none of his seven came in the 2-0 win over former club Arsenal.
Mourinho would perhaps have stuck with the same side for consecutive London derbies had it not been for an injury picked up by Andre Schurrle, who withdrew from Germany's 1-1 draw with the Republic of Ireland.
Willian travelled to Brazil and back this week, but is still the most likely candidate to replace him, with compatriot Ramires still sidelined. Loic Remy and Mohamed Salah are other options for the league leaders.
Thibaut Courtois recovered from the head injury which eventually forced him off against the Gunners to play two Euro 2016 qualifiers for Belgium and he will reclaim the goalkeeping jersey from Petr Cech.
Their 2-0 defeat to Hull City last time out was Palace's first loss in five top-flight games under Neil Warnock, but the journeyman manager is unlikely to panic into changing what has been a settled side.
The prognosis for Scott Dann looks good after he was stretchered off at the KC Stadium and, while this game comes too soon for the defender, Eagles medical staff are optimistic that he could play next weekend.
Adrian Mariappa is also a fitness doubt and therefore Brede Hangeland could be handed a first Premier League start of the Warnock reign, having found himself surprisingly out of favour since the 65-year-old's return.
Possible starting lineups
Palace: Speroni; Ward, Hangeland, Delaney, Kelly; Jedinak, McArthur, Ledley; Puncheon, Bolasie, Campbell
Chelsea: Courtois; Ivanovic, Terry, Cahill, Azpilicueta; Matic, Fabregas; Willian, Oscar, Hazard; Costa
Sports Mole says: 0-2