Match ends, West Bromwich Albion 2, Chelsea 3.
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 at the break.
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 their captain's 54th-minute 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 Pedro provided them with enough inspiration to build the foundations for an edgy win, though they were given an early let-off after Nemanja Matic tripped Callum McManaman for the early spot-kick.
Man of the match Pedro inspires on debut
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 for the second, the attack stemming from a West Brom corner.
As the game wore on, Pedro's influence faded before he was replaced six minutes from time, but it was more to do with Chelsea being reduced to 10-men after Terry's shaky start to the second half.
Further questions over Terry
Having been substituted at half-time against Manchester City last Sunday, Terry was included alongside Kurt Zouma at the heart of the central defence as Gary Cahill made way.
But England international Cahill was on the field by the 56th minute following Terry's dismissal where he was outpaced by West Brom's record £12m signing Rondon, who was making his full debut after signing from Zenit St Petersburg.
The Venezuelan international had already set up Morrison's first goal before he latched onto Chris Brunt's through ball and was tugged back by 34-year-old Terry, who was sent off for the first time in the Premier League since 2010.
Despite the Chelsea skipper's complaints, referee Mark Clattenburg appeared to make a good decision as Rondon bore down on goal with the initial contact coming outside the penalty area.
Rondon's resulting free-kick was deflected over but he made an encouraging debut.
Rondon shows promise in place of Berahino
Rondon's inclusion came after West Brom boss Tony Pulis took the decision to leave Saido Berahino out of his squad following interest from Tottenham, who are reported to have had a £15m bid rejected by the Baggies.
Pulis complained before the game about the transfer window affecting players' concentration but the manager will have been buoyed by Rondon's display.
The former Crystal Palace and Stoke manager accepted criticism for playing with two strikers in their opening defeat by Manchester City, but he was far more cautious on this occasion and did not introduce forward Rickie Lambert until Chelsea were down to 10 men.
He could look back on Berahino's omission with some regret, though. As their regular penalty taker, he may have saved Morrison's early embarrassment, particularly as the Scottish international insisted on taking the spot kick ahead of Brunt after a lengthy discussion.
'Transfer window very unsettling for Berahino'
West Brom boss Tony Pulis on Saido Berahino's omission: "I had a chat with him yesterday and it's very unsettling. He's a great lad but he is a young lad. I just cannot believe we are talking about something that is not even going to happen today affecting the kid.
"We should all be talking about the football. The transfer window should close and the season should start and everybody should be talking about football and not other things.
"We have been working hard to try and bring players in but this all could have finished three weeks ago."
'People love Chelsea to lose'
Chelsea boss Jose Mourinho: "Many people in this moment are disappointed in this result. People love Chelsea to lose a game.
"The performance was not dramatic, not bad but obviously four points in three matches is not enough. It's our first step, three points. There is a feeling we are fighting against a lot but today we won."
The stats you need to know
- John Terry's red card was his first in the Premier League since April 2010 and his fifth overall.
- This is the first time James Morrison has scored twice in a Premier League game. That total equals his tally from last season.
- This is the second time in Premier League history that three Spanish players have scored for the same team in the same game since Michu, Pablo Hernandez and Angel Rangel scored for Swansea against QPR in February 2013.
- 19McManamanBooked at 71minsSubstituted forGnabryat 78'minutes
- 7MorrisonSubstituted forGardnerat 88'minutes
- 14McCleanBooked at 37minsSubstituted forLambertat 60'minutes
- 26TerryBooked at 54mins
- 21MaticBooked at 17mins
- 17PedroSubstituted forMikelat 84'minutes
- 22WillianSubstituted forCahillat 56'minutes
- 10E Hazard
- 19Diego CostaSubstituted forFalcaoat 78'minutes
- Mark Clattenburg
- Shots on Target
Second Half ends, West Bromwich Albion 2, Chelsea 3.
Foul by Branislav Ivanovic (Chelsea).
Craig Gardner (West Bromwich Albion) wins a free kick in the defensive half.
Attempt missed. Jonas Olsson (West Bromwich Albion) header from the right side of the box is just a bit too high. Assisted by Serge Gnabry with a cross following a corner.
Corner, West Bromwich Albion. Conceded by Thibaut Courtois.
Attempt saved. Salomón Rondón (West Bromwich Albion) right footed shot from the right side of the six yard box is saved in the centre of the goal.
Foul by Falcao (Chelsea).
Boaz Myhill (West Bromwich Albion) wins a free kick in the defensive half.
Corner, Chelsea. Conceded by Gareth McAuley.
Eden Hazard (Chelsea) wins a free kick on the left wing.
Foul by Serge Gnabry (West Bromwich Albion).
Substitution, West Bromwich Albion. Craig Gardner replaces James Morrison.
Attempt missed. Chris Brunt (West Bromwich Albion) right footed shot from outside the box is too high. Assisted by Claudio Yacob.
Attempt missed. Eden Hazard (Chelsea) left footed shot from the left side of the box is close, but misses to the right. Assisted by Nemanja Matic.
Attempt saved. Serge Gnabry (West Bromwich Albion) right footed shot from outside the box is saved in the centre of the goal. Assisted by Claudio Yacob.
Substitution, Chelsea. John Obi Mikel replaces Pedro.
Pedro (Chelsea) wins a free kick on the right wing.
Foul by Chris Brunt (West Bromwich Albion).
Attempt missed. Serge Gnabry (West Bromwich Albion) right footed shot from the left side of the box is high and wide to the right. Assisted by Chris Brunt following a corner.