A Chelsea performance that fizzled out in the second half as the Lancashire rain began has ended a bad week for Blues.
At half-time it was hard to see any result but an away win after Didier Drogbahad struck early and Carlo Ancelotti's team had remained almost untroubled at the other end. Looking to make amends for the Champions League exit, further chances had not been taken by the visitors in that opening period but little did we realise then how much that would cost.
The warning was there immediately after the break as Blackburn came very close to equalising but it was only a respite until the 24th minute of half of which Chelsea had lost control, El-Hadji Diouf levelling.
We infrequently threatened to take the lead again as a visit to the north-west of England cost points for the fourth time this campaign. Blackburn have been strong at home in recent weeks but gave a debut to 17-year-old Phil Jones at centre-back. From a Chelsea point of view this was not the bounce-back we were all looking for following Tuesday night. 
In two changes from that Inter defeat, Kalou was introduced to the starting line up to play on the left of an attack that lost Malouda to midfield. The France international was called upon to take the place of injured Ballack. Ferreira replaced Zhirkov at left back.
Blackburn v Chelsea
Ross Turnbull was asked to come and claim on a couple of early occasions when the home side attacked while at the other end Drogba curled a low shot wide.
With his next chance the Ivorian sidefooted his side into a fifth-minute lead. Anelka may have been short of a goal of late but he wasn't short of an impact in this move, finding his way past two Blackburn players on the left and squaring to his attacking colleague 15 yards out.
Blackburn v Chelsea
It was Drogba's 28th goal of the season. Kalou came close to his seventh and what would have been his first in the league when he headed over a Lampard corner just two minutes later.
Turnbull caught a Pedersen free-kick after Alex had fouled in a central position before Anelka should have at least worked stand-in keeper Brown after Kalou had shown Diouf a clean pair of heels. Salomon had temporarily switched to the right.
From another Lampard corner, Olsson blocked Alex's goalbound shot with his stomach after the Brazilian had connected well. Chelsea were looking dangerous with every attack.
Pedersen missed wildly on 25 minutes after another Alex foul gave Blackburn the chance to put the ball into the box.
With Chelsea's next attack, Lampard was just a whisker away from putting the ball on Kalou's head inside the six-yard box.
For a few minutes just past the half-hour the committed tackles began to fly in all around the pitch. It certainly roused a previously sudued home support.
Blackburn v Chelsea
When it returned to being about skill on the ball, Malouda made his way with pace through the middle of the Blackburn defence but having done the tough part, hit his shot too straight at Brown.
The only hitch in what was an otherwise straightforward first half for Ancelotti's team was an injury that forced Ivanovic off just before the break. He tangled with an opponent near the Blackburn byeline and although he continued after treatment, the Serb pulled up on his next run. Zhirkov came on with the purple-and-pink-booted Ferreira moving to the right.
The second half began with a fright when Turnbull couldn't find a way through a crowd and Samba headed a long throw over him. Fortunately Zhirkov was well-placed to head away from goal. Pedersen then shot over when Chelsea gave him a wide open space just outside the area.
Lampard woke his team-mates up by drifting a 30-yard shot wide of Brown's dive but just wide of the post.
Blackburn v Chelsea
The early high ball into the box had been a frequent Blackburn tactic and when Chelsea made a meal of dealing with one on 57 minutes, Pedersen was presented with a chance in a threatening position, but he failed to control it. It was a reminder that 1-0 is a slender lead.
Allardyce made his second sub just past the hour having earlier swapped Emerton for Dunn, and this was an unpopular one with the home support who jeered the decision to take off centre-forward Kalinic and bring on Roberts.
Pedersen wasted another opportunity after chesting a cross beyond Ferreira but Chelsea weren't to be let off the hook another time.
Again Blackburn tested the visitors by hitting space over on our right, Emerton crossing from deep, and Diouf rose above Ferreira to head in at the near post.
It was 1-1 and we had just over 20 minutes to keep the title race on track. Ancelotti made an immediate change by taking off Kalou and choosing Decorather than Joe Cole or Daniel Sturridge as the replacement. The shape shifted to a midfield diamond with the new introduction playing at the front of it.
Chelsea did apply pressure inside the final five minutes and Drogba struck a rocket of a volley from a corner that a defender somehow headed off the line and round the post. Zhirkov became the game's only booking late on.
Blackburn v Chelsea
Following defeats at Wigan, Manchester City and Everton, and now this draw, Lancashire has been an unhappy hunting ground this season, but if the most is not made of a long spell on top in a game, the risk of damage is always there. After a weekend when Manchester United and Arsenal both won, time will tell if this will be a result looked upon with much regret.
Chelsea (4-3-2-1): Turnbull, Ivanovic (Zhrikov 45), Alex, Terry (c), Ferreira; Lampard, Mikel, Malouda; Anelka (Sturridge 90), Kalou (Deco 73); Drogba.
Scorer Drogba 5
Booked Zhirkov 87
Blackburn (4-4-1-1) : Brown; Salgado, Samba (c), Jones, Olsson; Pedersen, Andrews, N'Zonzi (Hoilett 90+2), Diouf; Dunn (Emerton 55),Kalinić (Roberts 62).
Scorer Diouf 69.