Pedro gave the visitors the lead in the 20th minute after James Morrison had seen a penalty saved down the other end, before the Spaniard provided the assist for Diego Costa to double the champions’ lead on the half-hour mark.
Morrison somewhat made amends for his earlier miss to put the Baggies back in it five minutes later, but Cesar Azpilicueta restored the Blues’ two-goal lead three minutes before the break.
Chelsea looked to be in command until Terry was given his marching orders for bringing down Salomon Rondon on the edge of the box on 54 minutes, before Morrison scored again five minutes later to really worry Jose Mourinho on the Blues bench.
However, Chelsea managed to hold on to record their first win of the season, but this encounter provided further evidence that retaining their title, even with Pedro firing on all cylinders, will be anything but easy.
Pedro started for the Blues just days after joining from Barcelona, with Saido Berahino left out of the matchday squad for West Brom, with speculation mounting he could be about to sign for Tottenham.