In Week 30, Chelsea lost at home to West Bromwich. 
pixabay.com
"West Bromwich imposed their game on Chelsea
"Perhaps it was inevitable that the Londoners' unbeaten streak would end in a match against Allardyce's team. Having put things in order in his first few months at Chelsea, Tuchel watched things fall apart in a game with the team of a coach who loves nothing so much as proving his tactical skills against foreign coaches with great reputations. This was the APL in its exuberant, unruly, and utterly illogical form," writes Jake Steinberg in the pages of The Guardian.
"The Londoners can make no claims after being outplayed by Allardyce - the greatest expert on survival would fall out of the top four if Tottenham beat Newcastle on Sunday or West Ham beat Wolverhampton on Monday. They were a mess on all lines, and West Bromwich punished them for their shortcomings by responding to Pulisic's undeserved goal because they climbed seven points over 17th-ranked Newcastle thanks to the inspiring play of Mateus Pereira.
It wasn't just about Tiago Silva's red in the 29th minute. West Brom scored five goals on the power play, so Chelsea felt uncomfortable even before losing the Brazilian. Instead of viewing the defender's removal as an isolated setback, Tuchel acknowledged that it was because of Chelsea's problems with and without the ball."
Allardyce could save West Bromwich
"Robinson, who only came on the pitch in the 37th minute in place of the injured Branislav Ivanovic, immediately adapted to his team's momentum. His finishing shot in the episode of the third goal was the best of all time. Allardyce has never been out of the Premier League in his long coaching career, and if he maintains that record this season, it may be his greatest feat.
Chelsea's chances of qualifying for the Champions League have been dealt a blow
"Manager of the month in March and after a 14-match unbeaten streak, Tuchel must have thought that being Chelsea head coach was easy. But in terms of reality, it was as far-reaching as it could get and the German paid the price for his abruptness and fickleness, while a shocking blow was dealt with Chelsea's hopes of qualifying for the Champions League.
You've got to hand it to West Bromwich who has played brilliantly," says Matt Lowe in The Telegraph. "Substitute Callum Robinson, who came on as a substitute, would like to play with Chelsea every week as his double allowed the striker to score five goals in the Premier League.
Allardyce, who was once accused of playing '19th-century soccer' when he was West Ham's manager against Chelsea, is now the first coach to win at Stamford Bridge with three different clubs - Bolton, Crystal Palace, and West Bromwich.