Pedro struck a debut Chelsea goal to inspire the champions to their first win of the season at West Brom as John Terry's wretched campaign continued.
The Spain winger opened the scoring following his reported £21million move from Barcelona to set up a thrilling 3-2 win for the 10-man visitors.
Diego Costa and Cesar Azpilicueta also netted before Terry was sent off for bringing down Salomon Rondon after the break.
The skipper retained his place despite being hauled off in Chelsea's 3-0 defeat at Manchester City last week but doubts will grow over his future under Jose Mourinho.
James Morrison missed a first-half penalty but still scored twice as the Baggies gave Chelsea a scare, but they are still looking for their first win of the Barclays Premier League season.
Thibaut Courtois returned from suspension while Kurt Zouma replaced the axed Gary Cahill, who dropped to the bench.
Saido Berahino was dropped by Baggies boss Tony Pulis, who decided the striker was not in the right frame of mind after Albion rejected a bid from Tottenham.
The England Under-21 forward is understood to have been happy to play but Pulis opted to replace him with £12million record signing Rondon.
James McClean and Callum McManaman also started and McManaman taunted Chelsea in the hosts' fast start and won a penalty after 14 minutes.
The ex-Wigan man darted into the box and lured Nemanja Matic into a clumsy tackle which sent the winger sprawling and referee Mark Clattenburg pointed to the spot.
Berahino would have been on penalty duties had he played, so instead Morrison stepped up and his drilled effort was turned over by Courtois' trailing leg.
The Baggies were on top, though, with Chelsea's only danger coming from Costa, who fired an early shot wide.
Craig Dawson headed over after 17 minutes but the visitors look the lead as Pedro made an immediate impact.
He had been quiet but burst to life when Eden Hazard found him on the edge of the box and his shot deflected in off Gareth McAuley.
From then, Chelsea took control and went 2-0 up on the half-hour following a counter-attack of ruthless precision.
Terry headed an Albion corner clear to Branislav Ivanovic, who found Willian scampering clear. The midfielder picked out Pedro and his cross-shot was finished by the unmarked Costa.
The champions looked set for a Sunday stroll at The Hawthorns but Morrison made amends for his penalty miss by dragging the hosts back into the game.
McClean launched a deep cross to Rondon, who acrobatically cut the ball back to Morrison to fire in from 15 yards.
But the visitors regained their composure three minutes before the break.
The disappointing Cesc Fabregas lofted a clever ball to Costa who, wrestling with McAuley, worked it to the unmarked Azpilicueta to find the corner from 15 yards.
Any hopes Chelsea had of a comfortable win went out the window however when Terry was sent off nine minutes after half-time.
The defender allowed Rondon to escape after Chris Brunt's excellent ball and clipped the striker, who was clean through, leaving Clattenburg little choice.
Five minutes later and the Baggies grabbed a lifeline when Morrison claimed his second with a fine header from Brunt's cross which flew in off the bar.
The champions were on the back foot as Rondon and McManaman went close while Costa had the chance to finish the game but fired over with 14 minutes left.
Hazard dragged wide and Courtois saved Chelsea in stoppage time when he produced a fine point-blank block to deny Rondon an equaliser.
TWEET OF THE MATCH
"John Terry could elongate his career if he continues on a part time basis." - Gary Lineker looks on the bright side after Chelsea defender Terry is sent off.
Boaz Myhill: 6 (out of 10)
Craig Dawson: 6
Gareth McAuley: 6
Jonas Olsson: 6
Chris Brunt: 6
Claudio Yacob: 6
Darren Fletcher: 6
James McClean: 6
James Morrison: 7
Callum McManaman: 7
Salomon Rondon: 6
Rickie Lambert: 6
Serge Gnabry: 6
Craig Gardner: 6
Thibaut Courtois: 8
Branislav Ivanovic: 8
John Terry: 5
Kurt Zouma: 7
Cesar Azpilicueta: 7
Nemanja Matic: 6
Cesc Fabregas: 6
Eden Hazard: 7
Diego Costa: 7
Gary Cahill: 6
Radamel Falcao: 6
John Obi Mikel: 6
The Chelsea new boy looked like he had been a Blues player for years with a debut of pace, precision and quality.
His opening goal and assist underlined his quality but workrate and commitment to the cause should not go unnoticed.
It will be Manchester United's loss that they failed to sign the winger from Barcelona as he gave a glimpse of what he will offer Chelsea in the title race.
The Hawthorns on a wet Sunday afternoon is not the most glamorous place for a debut for someone used to the Nou Camp but Pedro proved his worth.
MOMENT OF THE MATCH
Chelsea doubled their lead after half an hour with a lightning break and gave the Baggies a mountain to climb.
John Terry's initial header from Chris Brunt's corner found Branislav Ivanovic who, in turn, fed Willian.
The midfielder's touch was crucial as he got it out of his feet to find Pedro and his cross shot was turned in by Diego Costa.
It wrestled control of a game which could have been so different had Thibaut Courtois not saved James Morrison's early penalty.
VIEW FROM THE BENCH
Jose Mourinho would have been troubled by Chelsea's start as they were on the ropes and survived a let-off when Courtois saved Morrison's penalty.
But he would have been delighted with the response and impact new signing Pedro made once he scored a debut goal on 20 minutes.
Tony Pulis continues to search for a win at West Brom boss this season - and has pointed out their tricky start - but the Baggies need to get their campaign up and running.
MOAN OF THE MATCH
Terry continued his stuttering season after being sent off after the break at The Hawthorns.
The defender got himself into all kinds of trouble up against Salomon Rondon and allowed the striker to get goal side.
There will be a doubt over whether the forward would have got the ball ahead of Courtois but referee Mark Clattenburg had little option at first glance.
After retaining his place despite being replaced at half time at Manchester City last week, Terry could find it tough to return to the side after suspension.
WHO'S UP NEXT
Chelsea v Crystal Palace (Premier League, Saturday August 29)
West Brom v Port Vale (Capital One Cup, Tuesday August 25
Chelsea boss Mourinho swerved questions about Terry's red card and instead chose to hail what he thought was a fantastic performance from his side.
"I prefer not to think. I prefer to do what I'm doing or trying to do since the beginning of the championship which is to focus on the game," the Portuguese said when asked about his captain's sending-off.
"(It was a) fantastic performance. When we had the ball we were always dangerous and the three goals are short for the chances that we created for the football we played.
"After that with 10 men, the spirit and the fight in the defensive areas was very tough. More than happy."
Fabregas admitted all that mattered to Chelsea ahead of kick-off was recording their first victory of the Premier League campaign.
Before the win over the Baggies, the Blues were held to a 2-2 draw by Swansea and lost 3-0 against Manchester City.
"One hundred per cent today was about winning, about getting the points and getting back on track," the Spain international said.
"We made it in difficult circumstances. It looks every time that we had a comfortable game and were dominating that something happens lately.We bounced back in a difficult situation.
"We work hard and we have to keep going, and before the international break we want six points."