Brentford exposed Chelsea's defensive problems to inflict a damaging 3-0 defeat on Friday that gives Xabi Alonso plenty to ponder over a three-week international break.
After a promising start to life under the former Real Madrid coach, Chelsea have picked up just one point from their last three league games.
Goals from Jaidon Anthony, Igor Thiago and Fabio Carvalho took unbeaten Brentford above their west London neighbours and up to third in the table.
"I have this unbelievable calm around that team because I trust them. It's nice to see it come to fruition," said Brentford boss Keith Andrews.
Chelsea had quickly earned the reputation as the Premier League's great entertainers under Alonso with their opening four games containing 19 goals.
But the loss of Joao Pedro to a knee injury subdued the Blues' free-flowing attack as Cole Palmer and Morgan Rogers were comfortably kept in check by the Bees.
"At the moment we are not being consistent enough to compete during the whole game," said Alonso.
"It's about everything. It's about the mentality. It's about football, tactical things that we need to keep improving that we can do much better."
Alonso said after last weekend's 2-2 draw against Hull he was hoping for more "boring" games going forward.
The Spaniard sought control as he made four changes in all, handing Jordan Henderson his first Chelsea start against the 36-year-old's former club.
Alonso got his wish during a flat first half in which neither goalkeeper was seriously tested, but Brentford were the more threatening side in the second period.
The visitors' frailty from set-pieces led to the opening goal when Jannick Schuster rose highest to meet Mikkel Damsgaard's corner and Anthony was left with a simple task to head into an unguarded net just after the hour mark.
Chelsea's response was muted and as they pushed forward in search of an equaliser, Alonso's men were picked off on the counter-attack.
Kevin Schade should have scored the second goal himself when played clean through on Emi Martinez.
But even after the Argentine goalkeeper spread himself to save, the rebound fell kindly for Thiago to end his goal drought.
The Brazilian netted 25 times last season, earning a shock call-up to Carlo Ancelotti's World Cup squad as a result.
Thiago has looked shorn of confidence in the early weeks of the campaign and tore off his shirt in celebration after netting for the first time in the Premier League this season.
Chelsea have conceded at least twice in all five league games under Alonso and there was further punishment to come in stoppage time.
Schade's low cross was deflected into the path of Carvalho who fired high past Martinez to leave Andrews yelling into the night sky in delight.
Brentford, who also beat Tottenham 3-0 on the opening weekend of the season, sit behind only defending champions Arsenal and Manchester City at the top of the table.
By contrast, Chelsea were handed another reminder of the gap Alonso must bridge to make them title contenders once more.
