Match ends, Arsenal 1, Leeds United 0.
Arsenal manager Mikel Arteta "shouted a lot" at half-time to inspire an improved performance that helped the Gunners beat Leeds United and progress to the FA Cup fourth round.
Leeds dominated before the break, with Patrick Bamford hitting the bar with one of United's 15 first-half efforts.
Arsenal were excellent in the second half and Reiss Nelson scrambled home to secure a second consecutive win.
The Gunners will visit Bournemouth in the next round later this month.
Arsenal keeper Emiliano Martinez said Arteta was "really angry" at the break and striker Alexandre Lacazette told BBC One: "The manager shouted a lot. He was not happy because we knew they'd play like this and we didn't respect what he had said."
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The hosts had the majority of the second-half chances, with Lacazette clipping the crossbar with a free-kick.
"Now I'm really pleased but we saw two different teams - one in the first 30 minutes, and another after that," said Arteta.
"I tried to tell them exactly what they were going to face and after 32 minutes we had won one duel, I think. We changed our attitude, desire and organisation at half-time and then we were completely different.
"Sometimes they have to experience themselves how tough and how hard it is going to be. I watched a lot of Leeds games and they battered every team every three days. It was good for my players to learn and to suffer on the pitch."
Leeds boss Marcelo Bielsa will see the game as a missed opportunity for the Championship leaders - especially after their first-half performance - although he can now focus on promotion and ending the club's 16-year absence from the top flight.
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Arsenal manage to turn it around
Arteta said in the build-up that Arsenal had to take the FA Cup "very seriously" and become "addicted" to winning, naming a strong team.
They came into the game on the back of one of their most impressive performances of the season. They were excellent in the first half of their 2-0 win over Manchester United on New Year's Day, although faded after the break.
This was the exact reverse.
The 13-time FA Cup winners were abject in the first half - with only 37.2% possession and one shot on target - and could have been out of the game before half-time.
BBC pundit Alan Shearer said Arsenal "turned up in the first half and thought 'we don't have to run around'".
Former Premier League striker Chris Sutton, speaking on BBC Radio 5 Live, said: "The first half was just so flat. Was it a lack of effort? It looked that way."
Whatever was said by Arteta at the break worked perfectly and they were a team reborn in the second half.
Nicolas Pepe fired over a shot just seconds after the restart as they immediately expressed their intent. Lacazette forced a save from Illan Meslier and then struck the bar with a free-kick.
Lacazette had a hand in the goal as his cross was deflected by Gaetano Berardi into the path of Nelson, whose scuffed shot just went in.
"The emotions are high," said Nelson after scoring his second goal of the season. "They played well in the first half. Leeds are a great team and they pressed us, we didn't expect it. We got the goal in the end and that is the most important thing.
"This will give us confidence to go forward."
There was only one winner from the moment Nelson scored and substitute Gabriel Martinelli drew a good save from Meslier with a 20-yard drive.
The hosts did have a scare when VAR checked whether Lacazette should be sent off for violent conduct after appearing to kick out at Berardi but he escaped punishment.
Leeds will take heart into promotion bid
Bielsa said he was taking the cup seriously, although handed debuts to two players - French teenage goalkeeper Meslier and 20-year-old midfielder Robbie Gotts - both of whom did well.
They are nine points clear of third-placed Brentford in the Championship and hoping to avoid a repeat of their late-season collapse from last year.
Based on this performance - and a rowdy away following of 8,000 fans - they would be a wonderful addition to the Premier League.
In the first half at Emirates Stadium they were magnificent, dominating possession and territory, creating plenty of chances and putting Arsenal under constant pressure whenever they had the ball.
They looked nothing like a Championship team away from home against a "big-six" side.
Bamford had three shots in the opening 10 minutes before smashing the crossbar after playing a one-two with the lively Jack Harrison.
Harrison had a 20-yard curling effort saved by Martinez and after 17 minutes Leeds boasted seven shots to Arsenal's one.
The pressure kept on coming. Ezgjan Alioski drove a shot just wide and then his header was kept out by the busy Martinez.
They must have wondered whether they would be made to pay for missing their chances - and they were.
Their performance dipped in the second half as Arsenal upped their game, and they never looked like mounting a comeback after Nelson bundled home.
"What we needed to do in the match is repeat what we did in the first half," said Bielsa.
"The first half was very, very positive for us. In the second half the control of the match changed a lot.
"In the first half we pressed the opponents' defence more and were able to attack fast. We couldn't do that in the second half."
Man of the match - Alexandre Lacazette (Arsenal)
Match stats - Arsenal win two in a row for first time since October
- Arsenal have won eight FA Cup games against Leeds - only against Wolves and Chelsea (nine each) have the Gunners won more matches in the competition.
- The Gunners remain unbeaten in their last seven matches against Leeds (W6 D1), since a 3-2 defeat at Highbury in the Premier League back in May 2003.
- Leeds have won just one of their last 12 FA Cup matches away from home against top-flight opposition (D3 L8), a 1-0 victory against Manchester United at Old Trafford back in January 2010.
- That was their only clean sheet in their last 19 FA Cup games against top-flight sides.
- Arsenal have won back-to-back matches for the first time since October (against Standard Liege and Bournemouth), which was also the last time they kept consecutive clean sheets.
- Reiss Nelson has been directly involved in four goals in his last four starts for Arsenal at the Emirates Stadium in all competitions - two goals and two assists.
- Leeds attempted 15 shots in the opening 45 minutes against Arsenal, the joint most shots the Gunners have faced in the first half of a game this season.
Arsenal visit Crystal Palace in the Premier League on Saturday (12:30 GMT), while Leeds host Sheffield Wednesday in the Championship at 15:00.
- 23David Luiz
- 31KolasinacBooked at 71mins
- 19PépéSubstituted forSakaat 90+1'minutes
- 10ÖzilSubstituted forWillockat 77'minutes
- 24NelsonSubstituted forMartinelliat 67'minutes
- 2AylingSubstituted forStevensat 78'minutes
- 36GottsSubstituted forDallasat 60'minutesBooked at 85mins
- 43KlichBooked at 66mins
- 10AlioskiSubstituted forHélder Costaat 61'minutes
- 17Hélder Costa
- Anthony Taylor
- Shots on Target
Second Half ends, Arsenal 1, Leeds United 0.
Kalvin Phillips (Leeds United) wins a free kick in the defensive half.
Foul by Gabriel Martinelli (Arsenal).
Hélder Costa (Leeds United) wins a free kick in the defensive half.
Foul by Matteo Guendouzi (Arsenal).
Attempt missed. David Luiz (Arsenal) right footed shot from outside the box is too high from a direct free kick.
Foul by Hélder Costa (Leeds United).
Matteo Guendouzi (Arsenal) wins a free kick in the attacking half.
Substitution, Arsenal. Bukayo Saka replaces Nicolas Pépé.
Mateusz Klich (Leeds United) wins a free kick in the defensive half.
Foul by Matteo Guendouzi (Arsenal).
Jack Harrison (Leeds United) wins a free kick in the defensive half.
Foul by Sokratis (Arsenal).
VAR Decision: No card change Barry Douglas (Leeds United).
Foul by Jordan Stevens (Leeds United).
Granit Xhaka (Arsenal) wins a free kick on the right wing.
Stuart Dallas (Leeds United) is shown the yellow card for a bad foul.
Foul by Stuart Dallas (Leeds United).
Gabriel Martinelli (Arsenal) wins a free kick on the left wing.