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Guus Hiddink revealed his decision to substitute Baba Rahman at half-time in Chelsea's 2-1 Premier League win at Southampton owed entirely to the defender's poor performance, adding his left-back was not carrying an injury.
Rahman's soft header had just gifted Shane Long the chance from which he gave Southampton the lead and, despite Chelsea's limited options in defence, Hiddink decided he had seen enough.
The decision to replace Rahman with Kenedy paid dividends as second-half goals from Cesc Fabregas and Branislav Ivanovic secured victory, but despite Chelsea's improving form there must be concerns about the defence after Hiddink was forced to act.
"I could say he was injured, but he was just taken off because of that (mistake)," said Hiddink, who is already without Kurt Zouma and John Terry, while Pedro was lost to a hamstring injury after six minutes.
"I don't like to personalise it, but you have to take decisions sometimes that can appear very harsh. We have to cope with that.
"Young Kenedy did his job very well when he came in. Sometimes you have to take decisions like that. It's like it is. It's harsh, but I have also to control and not always wait on decisions. I'm responsible for the general result.
"I don't know what the 'old Chelsea' was, but the Chelsea we want to see is one that reacts when there is a setback. We like to be pro-active and show the desire is huge to turn a result from negative to positive. The players must respond, and they did."
Prior to Long's goal, Rahman had been criticised by Fabregas for giving the ball away, suggesting Hiddink is not the only one losing patience with a player signed for ?22million. That they were facing Ryan Bertrand, a player they sold to Southampton for ?10million, only highlighted his poor performance.
Chelsea's second-half goals ended Southampton's run of five wins from their previous six fixtures, while England goalkeeper Fraser Forster conceded for the first time in 708 minutes.
Manager Ronald Koeman insisted his side were unfortunate to fall to defeat but, although his team were denied a possible penalty for Gary Cahill's challenge on Charlie Austin with the score at 1-0, he refused to criticise referee Martin Atkinson.
"If you get a penalty, and make it 2-0... these are important decisions, but at the end of the season you get some situations that help you and others that don't," he said. "I don't complain about the referee or the linesman's performance.
"We played better at Chelsea (in October's 3-1 away victory) than we did (on Saturday). We played different.
"Chelsea are more confident at the moment, (their) players back at a better level, but it's my job to analyse Southampton, not Chelsea. We had more problems in the second half and they punished us for that."