Manchester City's Kevin De Bruyne, right, scores his side's second goal during the English FA Cup fourth-round soccer match between Leyton Orient and Manchester City at the Gaughan Group Stadium in London, England. (AP )

LONDON, Feb 8, (AP): Manchester City survived a scare against third-division Leyton Orient on Saturday to advance to the fifth round of the FA Cup.

Orient threatened to pull off a famous upset when it led 1-0 at halftime against Pep Guardiola's four-time defending Premier League champion.

But City fought back after the break with goals from substitutes Abdukodir Khusanov and Kevin De Bruyne.

"That’s why this competition is unbelievable,” Guardiola said.

Orient went ahead spectacularly when Jamie Donley's shot from just past the halfway line hit the bar and rebounded off the back of City goalkeeper Stefan Ortega into the back of the net in the 16th minute at Brisbane Road.

It was officially credited as an own goal, but Donley took the congratulations as he celebrated wildly in front of the home fans. He was also rewarded with the player-of-the-match award.

But the goal wasn't enough to hold off City's fightback.

Rico Lewis' effort deflected off Khusanov in the 56th to level the match and De Bruyne flicked a shot past Josh Keeley in the 79th to seal victory.

It wasn't all good news for Guardiola, however. $61.8 million midfielder Nico Gonzalez was injured and substituted after 22 minutes of his debut.

Leeds, top of division two, was knocked out by Millwall - losing 2-0 at home.

Harry Maguire scored a controversial injury-time winner as Manchester United came from behind to beat Leicester 2-1 and move into the last 16 of the FA Cup.

United went behind to a Bobby De Cordova-Reid goal four minutes before halftime. Joshua Zirkzee equalized in the 68th minute and Maguire grabbed the late winner.

There was a heated debate over whether the England center-half was in an offside position, but since there is no VAR in the FA Cup, the goal stood.