Earlier, Premier League leaders Arsenal stayed on track for a historic quadruple by seeing off a feisty challenge from third-tier Mansfield to win their fifth-round tie 2-1.

Pep Guardiola's City, who like Arsenal are still chasing glory on four fronts, were almost entirely changed from the side that drew 2-2 with Nottingham Forest in the Premier League in midweek, with only Matheus Nunes keeping his place.

Eddie Howe made a relatively modest four changes to his Newcastle team, fresh from their late win against Manchester United, with match-winner Will Osula given a rare start.

The home side began strongly at St James' Park and took a deserved lead when Harvey Barnes finished smartly after being found by Sandro Tonali.

City were level in the 39th minute in bizarre fashion when Jeremy Doku's dangerous ball behind the defence ran all the way to Savinho.

The Brazilian stood still and appeared to let the ball bounce off his leg into the net.

Soon after the restart City completed the turnaround when Omar Marmoush smashed the ball into the roof of the goal from close range.

The Egyptian forward then thundered home his second in the 65th minute to put his team in total control.

Guardiola, whose team travel to face Real Madrid in the Champions League on Wednesday, turned to a bench packed with international talent in the second half to refresh his side, who are seeking to reach their fourth straight FA Cup final.

"In Leverkusen, it was a strong squad too (a 2-0 defeat for a much-changed side), but we won today, so it was fine," Guardiola told the BBC. "It was a good decision and when I lose it was a bad decision.

"This is the best performance we have played in this stadium since my decade here. That is consistency and that is why I am proud."

- Chelsea scare -

Chelsea are also into the last eight after a 4-2 win but only after a mighty scare against second-tier Wrexham, who twice took the lead at the Racecourse Ground.

Hollywood-owned Wrexham, watched by actors Ryan Reynolds and Rob McElhenney, went ahead through Sam Smith but the visitors drew 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 Wrexham midfielder George Dobson was sent off in stoppage time and Chelsea winger Alejandro Garnacho volleyed home in the first period of extra time before substitute Joao Pedro's late strike added gloss to the scoreline.

Chelsea boss Liam Rosenior, who made nine changes with Wednesday's match against Paris Saint-Germain in mind, admitted his side had ridden their luck.

"That's the reason why the FA Cup is what it is," he said. "I thought Wrexham were magnificent -- magnificent in their energy, how brave they were and how they played.

"We had to be at a high, high level. We were pushed all the way by a very good team."

Wrexham boss Phil Parkinson, who has masterminded three straight promotions for his side, said they could take "a lot of heart" from the performance.

"We showed a lot of good aspects to our play and played some great football," he told the BBC. "We weren't just coming here to stop Chelsea -- we believe we can play."

Wrexham will now turn their attention to their push for a fourth straight promotion -- this time to the Premier League.

In the first FA Cup match of the day, Eberechi Eze smashed home the winner as a much-changed Arsenal toughed out a win against Mansfield.

Noni Madueke put the 14-time FA Cup winners ahead against the League One strugglers shortly before half-time, only for substitute Will Evans to level soon after the break.

England forward Eze thumped home midway through the second half to restore Arsenal's lead, minutes after being introduced by Arsenal boss Mikel Arteta.