Ronald Koeman says Chelsea's defence has lost some of its quality this season and he hopes Southampton can take advantage of that at Stamford Bridge.
The defending Premier League champions have been uncharacteristically shaky at the back this season, with mistakes creeping into their game and affecting their start to the campaign.
After coming from two goals down to draw 2-2 with Newcastle United last weekend, more errors allowed Porto to record a 2-1 win in the Champions League in midweek.
Koeman – who earned a 1-1 draw at Stamford Bridge last season – says there are more chinks in Chelsea's armour this season but does not expect an easy encounter on Saturday.
"Maybe they have lost a bit of that winning mentality," he said. "[And] they are making more changes [in defence] than last year.
"Everyone can have a tough start, maybe defensively they have lost a little bit [of quality], if you look at the goals they have conceded, it is a big difference to last year, so maybe they have lost a little bit.
"[But] we have to play on a higher level. We can't lose balls we lost last weekend [agaisnt Swansea City] because they will punish you.
"They have a very fast transition, you have to play compact and good counter-attacking football, and in all aspects have to be better than last year.
"We know we can have a good result if we play at our level because we had two draws against them last year, that belief we had last year we have to show again."
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