Timo Werner scored his first Premier League goals for Chelsea but they twice blew the lead to draw 3-3 with Southampton in a Premier League thriller.
The Germany striker had a goal disallowed for offside but a minute later opened his account with a lovely dummy before racing into the box, holding off four defenders and lashing it into the bottom corner.
The Saints had an attacking line-up, including a second debut for Theo Walcott 15 years after his first, but their tactics played into the Blues' hands and they went 2-0 up when Werner controlled Jorginho's looping pass and lobbed the ball over the keeper and headed it in.
Frank Lampard's side continued their onslaught and should have been further ahead but the visitors scored a goal out of nothing after a mistake from Kai Havertz with Che Adams threading the ball through to Danny Ings who rounded the recalled Kepa to make it four goals in four games.
Ralph Hasenhuttl's men capitalised on another comical Blues blunder involving Kepa in the second half to equalise with Adams eventually smashing the ball into the roof of the net.
But the home side were back in front two minutes later when Werner squared the ball for Havertz to his first goal for the club, echoing their link-up play for Germany in the 3-3 draw with Switzerland in midweek.
Hakim Ziyech came on for his league debut in the closing stages but Chelsea's performance levels and workrate dipped and the Saints equalised in the 92nd minute from Jannik Vestegaard's glancing header from Walcott's driven effort.
Chelsea's defensive woes continue. Lampard must be pulling his hair out after blowing a 2-0 lead then a 3-2 lead in stoppage time. It would be little surprise if Kepa has played his last game for the club after a shocking error for Adams' goal. Christensen and Zouma also had games to forget as it was a similar story for Lampard's side with individual errors costing them just as they did in the 3-3 draw with West Brom and 2-0 loss to Liverpool.
Edouard Mendy and Thiago Silva being unavailable did not help matters but the game showed some of the Blues' squad players cannot be relied upon.
MAN OF THE MATCH
Timo Werner (Germany): The wait for his first Premier League was worth it. It was the Timo show in the first half with two brilliantly taken solo efforts. His link-up play with Pulisic, Mount and compatriot Havertz was pulsating to watch.
Chelsea: Kepa 3, Azpilicueta 5, Christensen 4, Zouma 4, Chilwell 6, Kante 5, Jorginho 7, Mount 7, Havertz 8, Pulisic 6, Werner 9. Subs: Ziyech n/a, James n/a, Abraham n/a.
Southampton: McCarthy 5, Walker-Peters 4, Vestegaard 7, Bednarek 3, Bertrand 4, Romeu 5, Ward-Prowse 7, Redmond 6, Adams 8, Walcott 7, Ings 8. Subs: Tella n/a, Diallo n/a, Long n/a.
14' - DISALLOWED GOAL! Lovely bending cross from Chilwell for Werner with a header but its correctly ruled off-side by about half a yard.
15' - GOAL! Chelsea 1-0 Southampton. Fantastic goal, Werner collects Chilwell's pass and beats four defenders and lashes it in.
28' - GOAL! Chelsea 2-0 Southampton. Lovely looping ball from Jorginho for Werner who holds off his marker, lobs the ball over the keeper and nods it in.
42' - GOAL! Chelsea 2-1 Southampton. Havertz gives the ball away, Saints pounce and its through to Ings who rounds Kepa and scores, easy as you like.
57' - GOAL! Chelsea 2-2 Southampton. Zouma's header back to the keeper is a poor one. Kepa is second best to a 50-50 ball with Adams who smashes it into the net. Shambles.
59' - GOAL! Chelsea 3-2 Southampton. Werner is through and squares it to Havertz for a tap in for his first league goal for the Blues.
90'+2 - GOAL! Chelsea 3-3 Southampton. From Bertrand's set piece, Vestergaard heads it in from close range from Walcott's shot. What a comeback!
- Kepa Arrizabalaga has now made three errors leading to goals in just three Premier League appearances this season. At least two more than any other player in the competition.