Chelsea goalkeeper Petr Cech has warned his teammates that tomorrow will be a very dangerous time to visit Southampton.
The sides have already met on two occasions in 2013 - both in January.
The Blues won 5-1 at St Mary's in the FA Cup, but then threw away a two-goal half-time lead 11 days later, as they were held to a 2-2 draw in the Premier League at Stamford Bridge.
That game proved to be Nigel Adkins's last in charge of the Saints and Cech believes that the South Coast outfit have improved since the 48-year-old was replaced by Mauricio Pochettino.
"In football, everything is different - you can have a first half that is completely different from the second half," Cech told Chelsea's official website.
"In the away game against Southampton we were very effective, taking our chances, and then at home we had a very good half - but the last half an hour of the game we allowed them to come back into it. You cannot do that in the Premier League.
"They changed manager with Pochettino and they are more attacking, more organised with very good pressing which makes them more aggressive - and, in turn, more confident because of the success they've been having."
Southampton currently sit 16th in the Premier League table, while Chelsea are third.
