The Spain international scored in Chelsea’s 2-1 victory over Norwich City at Carrow Road on Tuesday night as the Blues extended their unbeaten run since Mourinho left Stamford Bridge in December.
The 28-year-old striker has scored 10 goals and has made six assists in 15 games in all competitions since Mourinho was sacked.
Former Arsenal defender Keown has explained why Costa has rediscovered his best form under Mourinho’s successor Guus Hiddink.
“He looks fitter and stronger than at the start of the season,” Keown told Daily Mail.
“But I have a funny feeling that he was one of a number of Chelsea players where Mourinho got into their heads too much. Jose felt he needed to get them out of their comfort zone for them to perform but he got that wrong.
“All he did was take their confidence away.”
The Portuguese’s successor Guus Hiddink has remained unbeaten in the Premier League since taking over the reins.
Costa scored 20 goals in 26 Premier League games as the striker helped to fire Chelsea to the English top-flight title in 2015.
Costa moved to Chelsea in a £32m deal from La Liga side Atletico Madrid in 2014 after a prolific spell at the Spanish club.
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