Chelsea avoided a major upset as they came from behind to overcome a brave Reading at Stamford Bridge.
A Frank Lampard penalty put the home side ahead before Pavel Pogrebnyak's steered header levelled matters.
Blues keeper Petr Cech fumbled a Danny Guthrie free-kick into his own net to gift Reading a shock lead.
David PleatFootball Analyst
"A very spirited display from Reading. They've done themselves proud in many ways. It was a patchy performance from Chelsea. The strange thing is that we've seen six goals but not that many goal efforts."
Gary Cahill's shot hauled Chelsea level and, after Fernando Torres tapped in when he appeared offside, Branislav Ivanovic got a fourth for the Blues.
In such an enthralling and absorbing game, it was a shame that what appears to be a mistake by the linesman for Torres's goal played such a crucial role in the eventual result, and undid so much of Reading's good work.
The Royals were on the verge of a famous upset against the European champions for much of the game and, while there was an element of fortune for Chelsea, they will see it as reward for their pressure and perseverance.
And, although the victory moved them to the top of the Premier League for the first time since November 2010, there was little sign of what was to come early on when Chelsea had a classy and authoritative air about their play.
They had Reading rocking and, if Ramires had squared the ball to an unmarked Torres rather than go for a left-foot shot which was saved, Chelsea might have been ahead sooner.
Chelsea pressure told - Di Matteo
Torres epitomised the confidence oozing through the home side when he nutmegged Jem Karacan and ghosted past a defender before his shot was diverted wide by centre-back Alex Pearce.
The goal Chelsea had threatened to produce finally came when the speed and subtlety of Eden Hazard's footwork mesmerised Chris Gunter into bringing the Belgian down.
Lampard smashed in the resulting penalty but, rather than Chelsea going on to overwhelm the Royals, the home side were stunned by Reading's fightback.
Width was the visitors' strength and, when Garath McCleary drilled in a cross, Pogrebnyak's expert header to the far post was beyond Cech's reach.
The equaliser helped the visitors grow in stature and, if Cech had little chance with Reading's opener, he was at fault for their second.
Chelsea skipper John Terry cynically fouled Jobi McAnuff and Guthrie's low, driven free-kick was spilled by a sprawling Cech into his own net.
Reading were showing no respect or reverence to their more illustrious hosts and a rattled home outfit might have gone further behind had an unmarked Pearce managed to get on the end of Ian Harte's diagonal free-kick.
Reading were holding their own but, as Chelsea exerted more pressure, the visitors eventually succumbed, although Adam Federici will feel he should have had stronger hands to palm Cahill's 25-yard shot wide.
Chelsea's passing and probing helped them engineer a lead with a third goal when Ashley Cole slid the ball across for Torres to sidefoot in, although there was more than a hint of offside about his position.
Ivanovic's effort came when he was set up for an easy finish by Hazard with Royals keeper Federici stranded after going up to the Chelsea end for a corner as the visitors searched for an injury-time equaliser.
Chelsea manager Roberto Di Matteo:
"It was a very entertaining game for the supporters. We started very well, certainly until they equalised which knocked us back a bit.
"We kept them under pressure and luckily got the equaliser which galvanised us and we kept going forward.
"I've not seen the replay [of the Torres goal]. I looked at the linesman straight away and he gave the goal.
"We are very pleased with six points after two games."
Full Time The game is over, as the referee blows his whistle.
Assist by Eden Hazard.
90:00 +4:33 Goal scored
Goal! - Branislav Ivanovic - Chelsea 4 - 2 Reading A goal is scored by Branislav Ivanovic from inside the six-yard box to the bottom left corner of the goal. Chelsea 4-2 Reading.
Inswinging corner taken right-footed by Ian Harte from the right by-line.
Emboaba Oscar gives away a free kick for an unfair challenge on Mikele Leigertwood. Ian Harte produces a shot on goal direct from the free kick, blocked by John Terry.
Free kick awarded for an unfair challenge on Hal Robson-Kanu by Emboaba Oscar. Ian Harte delivers the ball from the free kick left-footed from left wing, Raul Meireles manages to make a clearance.
Centre by Hal Robson-Kanu, save made by Petr Cech.
Foul by Danny Guthrie on Raul Meireles, free kick awarded. Free kick taken by Branislav Ivanovic.
Noel Hunt challenges Raul Meireles unfairly and gives away a free kick. Indirect free kick taken by Gary Cahill.
Adam Federici takes the free kick.
Substitution Garath McCleary leaves the field to be replaced by Hal Robson-Kanu.
Fernando Torres gives away a free kick for an unfair challenge on Noel Hunt.
Substitution Juan Mata leaves the field to be replaced by Raul Meireles.
Shot from just outside the area by Juan Mata goes over the bar.
Jobi McAnuff takes a shot. Comfortable save by Petr Cech.
The assist for the goal came from Ashley Cole.
80:37 Goal scored
Goal! - Fernando Torres - Chelsea 3 - 2 Reading Fernando Torres scores a goal from close range to the top right corner of the goal. Chelsea 3-2 Reading.
The ball is delivered by Ashley Cole,
Eden Hazard takes a shot. Alex Pearce gets a block in. Shot by Juan Mata from deep inside the penalty area misses to the right of the target.
The referee penalises Emboaba Oscar for handball. Ian Harte takes the direct free kick.
Centre by Jobi McAnuff.
Ian Harte takes the free kick.
Substitution Noel Hunt joins the action as a substitute, replacing Pavel Pogrebnyak.
Free kick awarded for a foul by Emboaba Oscar on Jobi McAnuff.
The ball is swung over by Branislav Ivanovic, Kaspars Gorkss manages to make a clearance.
Shot from just outside the area by Daniel Sturridge goes over the bar.
Effort on goal by Juan Mata from outside the area goes harmlessly over the bar.
Substitution (Reading) makes a substitution, with Adam Le Fondre coming on for Jem Karacan.
Shot from just outside the box by Juan Mata misses to the left of the goal.
Assist on the goal came from Eden Hazard.
68:52 Goal scored
Goal! - Gary Cahill - Chelsea 2 - 2 Reading Goal scored by Gary Cahill from outside the box to the bottom right corner of the goal. Chelsea 2-2 Reading.
Substitution Daniel Sturridge on for Mikel.
Unfair challenge on Eden Hazard by Garath McCleary results in a free kick. Eden Hazard restarts play with the free kick.
Eden Hazard takes a shot. Alex Pearce gets a block in. Effort from deep inside the area by Frank Lampard misses to the left of the goal.
John Terry takes the free kick.
Booking Pavel Pogrebnyak booked for unsporting behaviour.
Pavel Pogrebnyak concedes a free kick for a foul on Ashley Cole.
Gary Cahill fouled by Pavel Pogrebnyak, the ref awards a free kick. Free kick taken by Gary Cahill.
Corner taken left-footed by Danny Guthrie from the right by-line, clearance by Frank Lampard.
Emboaba Oscar takes a shot. Save by Adam Federici.
Ian Harte concedes a free kick for a foul on Eden Hazard. The free kick is swung in left-footed by Juan Mata.
John Terry restarts play with the free kick.
Booking Booking for Jem Karacan for unsporting behaviour.
Foul by Jem Karacan on Juan Mata, free kick awarded.
Substitution (Chelsea) makes a substitution, with Emboaba Oscar coming on for Ramires.
Corner taken right-footed by Frank Lampard, clearance by Jem Karacan.
Ashley Cole fouled by Pavel Pogrebnyak, the ref awards a free kick. Free kick taken by Ashley Cole.
John Terry delivers the ball, clearance made by Kaspars Gorkss.
Fernando Torres gives away a free kick for an unfair challenge on Chris Gunter. Adam Federici takes the direct free kick.
Danny Guthrie produces a cross, clearance made by John Terry.
Eden Hazard delivers the ball, comfortable save by Adam Federici.
Ramires produces a cross, clearance by Chris Gunter.
Shot from deep inside the area by Eden Hazard clears the bar.
Effort on goal by Branislav Ivanovic from just inside the penalty box goes harmlessly over the target.
The referee gets the second half underway.
45:00 +2:05 Half time
Half Time The half-time whistle blows.
The ball is sent over by Eden Hazard, Headed effort on goal by Fernando Torres from inside the penalty box misses to the right of the target.
John Terry concedes a free kick for a foul on Pavel Pogrebnyak. Ian Harte delivers the ball from the free kick left-footed from right channel.
Corner from right by-line taken by Ian Harte.
Inswinging corner taken from the left by-line by Danny Guthrie, Fernando Torres makes a clearance.
Eden Hazard takes a shot from just outside the penalty area clears the crossbar.
Free kick awarded for a foul by Mikel on Mikele Leigertwood. Kaspars Gorkss restarts play with the free kick.
Ian Harte challenges Ramires unfairly and gives away a free kick. Free kick taken by John Terry.
Jobi McAnuff takes a shot. Save by Petr Cech. Jem Karacan concedes a free kick for a foul on Eden Hazard. Free kick crossed by Juan Mata. Shot from deep inside the area by John Terry goes over the bar.
The ball is sent over by Jobi McAnuff, save made by Petr Cech.
Assist by Jobi McAnuff.
28:37 Goal scored
Goal! - Danny Guthrie - Chelsea 1 - 2 Reading Danny Guthrie scores a goal direct from the free kick from just outside the penalty area to the bottom left corner of the goal. Chelsea 1-2 Reading.
John Terry gives away a free kick for an unfair challenge on Jobi McAnuff.
Free kick awarded for an unfair challenge on Danny Guthrie by Ramires. Mikele Leigertwood restarts play with the free kick.
Jobi McAnuff gives away a free kick for an unfair challenge on Juan Mata. Direct free kick taken by Mikel.
Assist on the goal came from Garath McCleary.
24:06 Goal scored
Goal! - Pavel Pogrebnyak - Chelsea 1 - 1 Reading Pavel Pogrebnyak finds the net with a headed goal from inside the box. Chelsea 1-1 Reading.
Garath McCleary produces a cross,
Eden Hazard gives away a free kick for an unfair challenge on Chris Gunter. Direct free kick taken by Chris Gunter.
Juan Mata crosses the ball.
Corner taken left-footed by Ian Harte, save made by Petr Cech.
Assist on the goal came from Eden Hazard.
17:37 Goal scored
Goal! - Frank Lampard - Chelsea 1 - 0 Reading Placed penalty scored by Frank Lampard. Chelsea 1-0 Reading.
Chris Gunter gives away a Penalty for an unfair challenge on Eden Hazard.
Frank Lampard takes a shot. Alex Pearce gets a block in.
Handball by Pavel Pogrebnyak. Free kick taken by Mikel.
The assistant referee flags for offside against Pavel Pogrebnyak. Indirect free kick taken by John Terry.
Ramires takes a shot. Save made by Adam Federici. Fernando Torres takes a shot from 20 yards. Blocked by Alex Pearce.
Chris Gunter gives away a free kick for an unfair challenge on Eden Hazard. Direct free kick taken by Eden Hazard.
Foul by Mikele Leigertwood on Juan Mata, free kick awarded. Gary Cahill restarts play with the free kick.
Shot by Pavel Pogrebnyak from deep inside the penalty area misses wide to the left of the target.
Ramires takes a shot. Comfortable save by Adam Federici.
Free kick awarded for an unfair challenge on Alex Pearce by Fernando Torres. Adam Federici restarts play with the free kick.
Eden Hazard has an effort at goal from deep inside the area missing to the right of the goal.
Centre by Chris Gunter, John Terry makes a clearance.
The ball is swung over by Branislav Ivanovic, blocked by Jem Karacan.
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