Wrexham, watched at the Racecourse Ground by actors Ryan Reynolds and Rob McElhenney, took the lead through Sam Smith but the visitors were level courtesy of an own goal shortly before half-time.

In a breathless second period, Callum Doyle put the Welsh team back ahead again in the 78th minute only for Josh Acheampong to equalise four minutes later.

The game changed complexion when George Dobson was sent off in stoppage time and Alejandro Garnacho volleyed home in the first period of extra time before Joao Pedro's late strike added gloss to the scoreline.

Chelsea boss Liam Rosenior, juggling Premier League and Champions League commitments, made nine changes to his starting team against the Championship club.

In-form Wrexham, who put out Premier League club Nottingham Forest earlier in the competition, went ahead in the 18th minute when Doyle found Smith with a raking long pass.

Smith's first touch was superb and he raced away from Tosin Adarabioyo before finishing coolly past Robert Sanchez.

Chelsea enjoyed the bulk of possession but created little against Phil Parkinson's organised side, who are targeting a fourth-consecutive promotion -- this time to the Premier League.

But Wrexham suffered heartbreak five minutes before half-time when the ball squirmed into the net off the back of goalkeeper Arthur Okonkwo for an own goal.

Wrexham started the second half on the front foot again, putting Chelsea's defence under huge pressure, roared on by a passionate home crowd.

Rosenior brought on forward Marc Guiu for defender Mamadou Sarr just before the hour mark, throwing on Marc Cucurella and Dario Essugo a few minutes later.

Wrexham continued to make life uncomfortable for the Club World Cup champions and re-took the lead with a brilliant, instinctive flick from Doyle, who turned home Josh Windass's shot in the 78th minute.

But just minutes later Chelsea were all-square again, with Acheampong firing into the roof of the net.

Windass had a glorious chance to put Wrexham in front for a third time but headed wide with Sanchez stranded and Pedro Neto rattled the bar at the other end.

- Red card -

The dynamic of the match shifted when Dobson was sent off in stoppage time by referee Peter Bankes following a VAR review.

That gave Wrexham a mountain to climb and their task was even harder when Essugo's cross was finished crisply by Garnacho in the sixth minute of extra time.

Astonishingly, Wrexham had the ball in the net again after Kieffer Moore's header was turned home by Lewis Brunt but the goal was ruled out for offside by VAR.

Lewis O'Brien flashed just wide as Parkinson's side finally ran out of chances with substitute Pedro grabbing a fourth for Chelsea.

Chelsea now turn their attentions to a Champions League last-16 date with Paris Saint-Germain in midweek while Wrexham will continue their push to reach the Premier League.