Two goals from Saido Berahino and one from Chris Brunt ended Chelsea's 16-match unbeaten run in the English Premier League on Monday night.
West Bromwich registered a three nil win over their opponents at The Hawthorns, reports BBC.
Berahino's first strike came in the ninth minute, while his second came off a penalty strike. Chelsea veteran John Terry had brought him down minutes after the start of second half.
Chris Brunt completed the rout by scoring the third goal in 60th minute.
Chelsea's Cesc Fabregas was sent off after he kicked the ball at Brunt. Referee Mike Jones had to stop play at that point of time.
However, the result of the match was inconsequential as far as points were concerned, with Chelsea already crowned the 2014-15 EPL champions and West Bromwich comfortably sitting mid-table.