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Wrexham had pushed Chelsea all the way and twice led, but George Dobson's 93rd minute red card proved costly, as the Blues eventually got over the line.

The EFL Championship side stunned Chelsea in the 17th minute when Callum Doyle's long punt over the top was collected by Sam Smith, who took a touch before finishing beyond Robert Sanchez, with the Chelsea goalkeeper punished for his moment of hesitation.

However, for all its dominance, the home side was pegged back five minutes before the break in unfortunate circumstances as Garnacho's effort was cleared off the line by George Thomason, only for the rebound to cannon back off goalkeeper Arthur Okonkwo and in.

Chelsea turned the screw after the break, but found was behind once again in the 78th minute when Doyle instinctively flicked Josh Windass' strike at goal past Sanchez.

Josh Acheampong provided an almost instant response for Liam Rosenior's side, though, as he rifled the ball into the roof of the net just four minutes after the Blues went behind.

After Pedro Neto had rattled the crossbar, Wrexham's task was made even tougher when Dobson was sent off in second-half stoppage-time after a late and high challenge on Garnacho, his initial yellow card being upgraded after a video assistant referee (VAR) review.

Chelsea made its man advantage count six minutes into extra-time when Dario Essugo's pinpoint cross was volleyed home by Garnacho, though Wrexham gave the eight-time winner a scare in the 114th minute.

Lewis Brunt headed in at the back post after Kieffer Moore's flick from a corner, but Wrexham's joy was short-lived, with the goal ruled out for offside, with Chelsea making the most of that reprieve when Joao Pedro finished past Okonkwo in the 125th minute.

The influence of VAR – something EFL sides are not used to – was something Wrexham boss Phil Parkinson felt he had to comment on after the final whistle.

"It's such a shame, really, that our first taste of VAR has gone this way," he said.

"Immensely proud of the boys tonight. I thought we acquitted ourselves really well. I thought it was a tight game, which is a credit to us for that.

"We've got to be pleased with the pressing, the work, the discipline, but also some of the football we played.

"We carried a threat tonight, which we thought we would. We didn't just come here tonight to stop Chelsea. We knew we could play and we really did at times."

For Chelsea boss Liam Rosenior, the feeling was more relief.

"We're through," he said. "Not the best performance; really, really difficult game, which we knew it would be. Wrexham were outstanding.

"This was a proper FA Cup tie, the reason why everybody loves the FA Cup. I'm just delighted we're through in the end."