Lacazette's goals were his 12th and 13th in the Premier League this season and his fourth and fifth in his last six matches
Gabriel Martinelli scored in his first start since January as Arsenal ended a run of four games without a win with victory over the Premier League's bottom club Sheffield United.
The Brazilian has endured an injury-plagued season, but was on hand to net his side's second with a finish into an unguarded goal after Aaron Ramsdale had pushed out Nicolas Pepe's shot.
It was the 19-year-old's first goal since January 2020.
It came between two Alexandre Lacazette goals - the first a neat first-half finish after Dani Ceballos' back-heel and the second a clinical effort in the closing stages after he was put clear by Thomas Partey.
Sheffield United have won only four games this season and none since Paul Heckingbottom took caretaker charge a month ago and they had little answer to their opponents' increased efficiency.
At 1-0 there was always a chance that this generous Arsenal side may provide the Blades with a way back in, but Martinelli's strike ended such home hopes, with Lacazette adding the final flourish.
The win lifts Arsenal above Leeds and Aston Villa and up to ninth in the table, with 45 points.
It did come at a potential cost, though, with Bukayo Saka limping off in the second half, making him a possible doubt for the second leg of the Europa League last-eight tie with Slavia Prague on Thursday.
Sheffield United remain rooted to the bottom, 18 points from safety with just 21 left to play for. With their woeful goal difference, a loss at Wolves next Saturday will all but confirm their relegation.
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Morale-boosting win for Arsenal ahead of big European game
Arsenal endured a chastening eight days in the lead up to this fixture, suffering a humbling 3-0 loss to Liverpool in the Premier League before drawing the home leg of their Europa League quarter-final tie with Slavia Prague.
Their hopes of attaining a Champions League spot via a top-four finish are long gone, leaving success in Europe's secondary competition as their last remaining route back into its more lucrative big brother.
This game, then, was as much about getting Slavia's late equaliser at the Emirates out of their system with a more composed, confidence-boosting win.
It took them a bit of time to warm up to the task, but ultimately they found their stride, with Lacazette's opener coming during a period that saw Aaron Ramsdale tested and the side-netting struck.
Encouragingly, Martinelli, starting only his sixth game of an injury-plagued season, was at the heart of much of their attacking threat.
If he can stay fit for the remainder of the campaign, his excellent close control, direct running and eagerness to test an opposition goalkeeper could well make a big difference to a season currently finely balanced between success and disaster.
His re-appearance as a partner for the in-form Lacazette, who has five goals in his last six games, is timely in the absence of Pierre Emerick-Aubameyang.
Of some concern, though, will be the early departure of Saka from the game, with the talented young winger limping off after a challenge with Rhian Brewster.
The verdict on the Blades' season is already more or less set in stone.
They fleetingly offered the threat of creating something to worry the Gunners but ended with only wayward efforts from David McGoldrick and Brewster to really show for their efforts.
After 31 games that have highlighted that much of their squad is not equipped for the Premier League, the next seven will help them decide which players they want with them in the Championship next season.
More to follow.
- Line-upsMatch StatsLive Text
Line-upsSheff Utd
Formation 3-5-2
1Ramsdale22Ampadu12Egan3Stevens2Baldock7Lundstram16Norwood4Fleck23Osborn14Burke17McGoldrick
- 1Ramsdale22AmpaduBooked at 90mins12Egan3Stevens2Baldock7Lundstram16Norwood4Fleck23Osborn14BurkeSubstituted forBrewsterat 64'minutes17McGoldrickSubstituted forMcBurnieat 64'minutesSubstituted forMoussetat 83'minutes
Substitutes
- 9McBurnie11Mousset13Lowe15Jagielka18Foderingham20Bogle24Brewster29Bryan34Ndiaye
Arsenal
Formation 4-2-3-1
1Leno21Chambers16Holding22MarÃ34Xhaka18Partey8Ceballos19Pépé7Saka35Martinelli9Lacazette
- 1Leno21Chambers16Holding22MarÃBooked at 80mins34Xhaka18Partey8Ceballos19Pépé7SakaSubstituted forWillianat 69'minutes35MartinelliSubstituted forElnenyat 83'minutes9LacazetteSubstituted forNketiahat 89'minutes
Substitutes
- 2BellerÃn6Gabriel12Willian17Cédric Soares24Nelson25Elneny30Nketiah33Ryan66Azeez
Referee:Peter BankesMatch StatsHome TeamSheff UtdAway TeamArsenalPossessionHome45%Away55%ShotsHome7Away14Shots on TargetHome2Away5CornersHome2Away4FoulsHome9Away6Live TextPost update
Match ends, Sheffield United 0, Arsenal 3.
90'+5'Full Time
Second Half ends, Sheffield United 0, Arsenal 3.
90'+4'Booking
Ethan Ampadu (Sheffield United) is shown the yellow card for a bad foul.
90'+4'Post update
Eddie Nketiah (Arsenal) wins a free kick in the defensive half.
90'+4'Post update
Foul by Ethan Ampadu (Sheffield United).
90'+2'Post update
Foul by Rob Holding (Arsenal).
90'+2'Post update
Lys Mousset (Sheffield United) wins a free kick in the attacking half.
89'Post update
Foul by Eddie Nketiah (Arsenal).
89'Post update
Enda Stevens (Sheffield United) wins a free kick in the defensive half.
89'Substitution
Substitution, Arsenal. Eddie Nketiah replaces Alexandre Lacazette.
88'Post update
Attempt missed. Lys Mousset (Sheffield United) right footed shot from the centre of the box misses to the right. Assisted by Enda Stevens.
85'goalGoal!
Goal! Sheffield United 0, Arsenal 3. Alexandre Lacazette (Arsenal) right footed shot from the centre of the box to the bottom left corner. Assisted by Thomas Partey with a through ball.
83'Substitution
Substitution, Arsenal. Mohamed Elneny replaces Gabriel Martinelli.
83'Substitution
Substitution, Sheffield United. Lys Mousset replaces Oliver McBurnie because of an injury.
80'Booking
Pablo Marà (Arsenal) is shown the yellow card for a bad foul.
80'Post update
Offside, Sheffield United. Ben Osborn tries a through ball, but George Baldock is caught offside.
78'Post update
Attempt blocked. Rhian Brewster (Sheffield United) right footed shot from outside the box is blocked. Assisted by John Fleck.
76'Post update
Attempt blocked. Willian (Arsenal) right footed shot from a difficult angle and long range on the left is blocked.
75'Post update
Alexandre Lacazette (Arsenal) wins a free kick on the left wing.
75'Post update
Foul by Ethan Ampadu (Sheffield United).
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Source: bbc.com