John Terry was sent off as Pedro inspired Chelsea to a first Premier League win of the season at West Brom.
Thibaut Courtois saved James Morrison’s early penalty but Pedro, who signed from Barcelona for £21m this week, fired in before setting up Diego Costa.
Morrison then atoned for his earlier error with a crisp strike before Cesar Azpilicueta made it 3-1.
Terry saw red for a second-half foul on Salomon Rondon but Morrison’s header was not enough as Chelsea hung on.
The result ended a poor start to the season for Chelsea, who have raised as many talking points off the field as on it following controversy surrounding the treatment of their medical staff and Terry’s half-time substitution in the 3-0 loss at Manchester City last Sunday.
And in another eventful game for the champions, Jose Mourinho’s side will face further questions as Terry’s dismissal gave West Brom a huge lift following a first half where Tony Pulis’s team were outclassed at times.
Unlike their previous two games, though, Pedro provided them with enough inspiration to build the foundations for an edgy win.
After beating Manchester United to sign three-time Champions League winner Pedro, Chelsea benefitted from the 28-year-old’s pace and incisiveness as the club’s Spanish international contingent scored three times before the break.
Mourinho had criticised some of his players after earning only a point in their first two games, but Pedro gave their attacking an extra thrust, particularly on the counter attack.
Having already played alongside Cesc Fabregas while at Barcelona, the new recruit was heavily involved from the start, also linking well with Eden Hazard, who had his best game of the season so far after often coming inside to join-up with play.
It was from that combination that Pedro grabbed the opener, while his quick thinking was evident as he set up Costa from the second, the attack stemming from a West Brom corner.