Didier Drogba grabbed a hat-trick and France winger Florent Malouda scored twice as promoted West Brom, managed by former Chelsea midfielder Roberto di Matteo, were picked apart at Stamford Bridge.
"This was the perfect reaction to our bad pre-season," Malouda told the BBC. "It's important we start well because we are champions and everyone wants to beat us.
"To win like this reminds everyone that we are champions."
Malouda put Carlo Ancelotti's side ahead after six minutes and Drogba, like many of his team mates still not 100 percent fit after arriving back from the World Cup, 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.
Ancelotti played down Chelsea's pre-season hiccups, which included four consecutive defeats culminating in the Community Shield loss to arch-rivals Manchester United.
"We knew we had a problem," Ancelotti said. "We decided to give our players who played in the World Cup another six days of holiday.
"It was necessary for them to have a full recovery and we knew the first game of the pre-season we couldn't play them.
"John Terry, Ashley Cole and Frank Lampard also showed good condition today. Maybe they are still not in the best condition but in two weeks they will be 100 percent."
LAST SEASON
Chelsea have now scored 21 goals in their last three home league games, having thumped Wigan Athletic 8-0 and Stoke City 7-0 during their run-in to last season's title.
It was a chastening afternoon for Di Matteo, who was warmly applauded by the Chelsea fans.
"We have to learn quickly that the small details make a big difference in the Premier League," the Swiss-born Italian said.
West Brom's next three away games are at Liverpool, Arsenal and Manchester United.
"The fixtures are not kind to us, it's a tough start for any club to play those four away, but we'll pick ourselves up. We've still got 37 games to go," Di Matteo said.
