Didier Drogba grabbed a hat-trick and Florent Malouda scored twice as promoted West Brom, managed by former Chelsea midfielder Roberto di Matteo, were picked apart at Stamford Bridge.
Malouda put Carlo Ancelotti's side ahead after six minutes and Drogba doubled the lead with a free kick shortly before the interval.
The Ivory Coast striker grabbed his second after 55 minutes before Frank Lampard's clinical finish and another for Drogba with a deflected effort. Malouda completed the rout late on.
Chelsea have scored 21 goals in their last three home league games, having thumped Wigan Athletic 8-0 and and Stoke City 7-0 during their run-in to the title last season.
In the other matches, Manchester City unleashed around £70 million worth of signings as the Premier League kicked off on Saturday but it was Joe Hart, a keeper who cost nothing, who earned them a point in a 0-0 draw at Tottenham Hotspur.
Aston Villa were too good for a hapless West Ham, while Blackpool enjoyed a dream return to English football's top flight when they lit up the opening day of the Premier League season by thrashing Wigan Athletic 4-0.
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