Sheffield United staged a spirited second-half fightback to pick up a deserved 2-2 draw with Chelsea at Stamford Bridge.
After falling behind to Tammy Abraham's first-half double (19 and 43), the Blades responded with great confidence and character after the break.
Callum Robinson (46) swept home just after the break before his cross was deflected into the home team's net by Chelsea defender Kurt Zouma (89) to send the away end wild.
The result means Frank Lampard is still waiting for his first home win as Chelsea manager.
Chelsea: Arrizabalaga (6), Azpilicueta (6), Tomori (6), Zouma (6), Emerson (6), Jorginho (6), Kovacic (7), Pulisic (6), Mount (6), Barkley (5), Abraham (8)
Subs: Gilmour (6), Willian (5), Batsuahyi (6)
Sheffield United: Henderson (6), Basham (6), Egan (7), O’Connell (7), Baldock (7), Lundstram (6), Norwood (6), Freeman (7), Stevens (9), McBurnie (6), Robinson (8)
Subs: Mousset (7), McGoldrick (6)
Man of the match: Enda Stevens
How Wilder's men silenced Stamford Bridge...
Lampard, from the first whistle, was instructing Abraham to get down the side of the Sheffield United defenders. His willing running set Chelsea on the attack down the right in the 19th minute and he was on hand to open the scoring. Cesar Azpilicueta's cross was initially headed at goal by the striker and a fumble by 'keeper Dean Henderson - under pressure from Mason Mount - earned Abraham a second chance, which he took.
Fikayo Tomori replaced Andreas Christensen at the heart of the Chelsea back four, while Oli McBurnie was handed his first Premier League start for the club after making all three of his appearances from the bench so far for the Blades.
Despite bossing possession, Chelsea rarely opened the visitors up and it was the Blades who should have levelled on 39 minutes, but Robinson scuffed a close-range header wide after great work by Chris Basham.
It was a harsh lesson for Chris Wilder's men as a defensive mix-up handed Chelsea a two-goal lead minutes later. Jack O'Connell and John Egan challenged for the same ball which only diverted it straight to Abraham, who hammered into the corner from 15 yards.
Wilder got a dream start to the second period when Robinson pulled his team back into the match less than a minute after the break. Enda Stevens provided the creativity down the left and the former Preston man finished nicely from close range.
From that moment, Chelsea looked nervy at the back and rarely looked like adding to their tally up the other end, although Abraham was denied by a fine one-handed stop from Henderson on 58 minutes.
United continued to be brave with the ball, with Stevens a constant source of imagination down the left as Robinson almost converted from another wicked cross.
Lampard handed a Chelsea debut to 18-year-old Billy Gilmour in midfield from the bench, emphasising his embrace of the youth policy at the club.
However, Chelsea could not hold on and, with a minute to go, Robinson's cross caused problems for Zouma under pressure from Lyn Mousset and he deflected his clearance past his own goalkeeper.
Man of the match: Enda Stevens
Epitomised Wilder's approach: brave with the ball and tenacious without it. His fine break down the left just after half-time that set up Robinson's goal was the catalyst that sparked his team into life. His trickery and clever play down his flank made Cesar Azpilicueta - one of the great defensive full-backs - look very ordinary.
Manager reaction: Frank Lampard
"It's not just the defence - we concede as a team," Lampard said regarding Chelsea's defensive record.
"The lack of concentration and defensive mistakes are moments that you defend as a team. We conceded because we switched off in a game we should be comfortably seeing out. That's not disrespectful to Sheffield United as at 2-0 up that's not the end of the story. I was clear with the players at half-time.
"We only have ourselves to look at as a group, not individually."
Manager reaction: Chris Wilder
Wilder said: "We had to play well here, we can't give ourselves a mountain to climb, which we obviously did.
"To come roaring back as we did in the second half hopefully gives us an enormous amount of confidence and self-belief going forward.
"I don't want us to stand off teams, we obviously understand the teams we are up against and the journey we have been on.
"Three years ago we were bottom of League One and now we are going toe-to-toe in the Premier League. It's not a cup tie, we are here on merit.
"From a biased point of view, I believe we deserved something from our second-half performance."
Chelsea face a trip to Wolves after the international break, while Sheffield United host Southampton. Both are 3pm kick-offs on Saturday September 14.