Arsenal 2 Middlesbrough 0: Boro unable to get better of holders
The Gunners avoided going the same way as League champions Manchester City had against the Championship promotion-chasers with two first-half goals from the France forward in the space of as many minutes.
Giroud – out for three months earlier in the season with a broken fibula – blasted the ball past Boro goalkeeper Tomas Mejias from close range on 27 minutes and, before the visitors could recover, the forward sweetly volleyed home a corner.
Boro, who had been unbeaten in their previous 10 matches, worked hard enough, but never really stretched the Arsenal defence and have more important targets ahead over the closing weeks of the campaign in their bid to return to the elite.
Arsene Wenger’s side, meanwhile, look to have found form again just at the right time ahead of a crucial run of games, which sees them take on Monaco for a place in the last eight of the Champions League.
Arsenal set the tone with a positive start as Santi Cazorla tested Mejias with a curling 25-yard free-kick which almost crept inside the right-hand post.
Left-back Kieran Gibbs, one of several fringe players handed a chance to impress, was inches away from connecting with another pass slid into the Boro penalty area as the home side remained on the offensive.
Giroud had Mejias scrambling across his goal again on 14 minutes to palm a curling shot away acrobatically, with Alexis Sanchez, who had been a doubt because of a knee problem, putting the rebound into the side netting from the tightest of angles.
Boro, though, continued to defend resolutely, while also starting to offer a threat on the counter themselves.
However, Arsenal finally made their possession count on 27 minutes.
Cazorla, who had been running the game from a deep central role, picked out the overlapping Gibbs, who played a first-time pass into the six-yard box.
Giroud timed his run perfectly to blast the ball off the goalkeeper and into the net.
Before the Championship side could recover, it was 2-0.
As everybody waited on the edge of the penalty area, Sanchez played a quick corner in from the left, which Giroud ran onto ahead of George Friend to volley past Mejias at the near post for his 10th goal of the season.
Boro were in danger of being overrun, as Adam Clayton made a goalline clearance after Sanchez almost finished off another sweeping Arsenal attack from Mesut Ozil’s through-ball.
When the Championship side were able to relieve the pressure temporarily, Albert Adomah’s 25-yard pot-shot was straight at Wojciech Szczesny, the Pole returning to the side in place of David Ospina.
Arsenal, who had laboured to a Premier League win over bottom club Leicester at home in midweek, remained on the offensive in the second half.
Danny Welbeck’s angled chip dropped across the face of goal after more clever play from Giroud down the right.
Gabriel, making his debut, collected a first caution in English football when the former Villarreal defender clattered into Adam Reach as the Boro substitute broke quickly down the left.
As the hour mark passed, Mejias turned a rising drive from Gibbs over and then somehow got down to brilliantly tip away a glanced header from Sanchez as the ball looked to be dropping into the far corner.
Boro, though, still fancied their chances of getting back into the tie and Gabriel had to make a couple of important clearances.
It was almost 3-0 when Kenneth Omeruo blocked a bullet header from substitute Theo Walcott on the line, the England forward then being denied by a save from Mejias after bursting clear down the right.
In stoppage time, a far-post header from Kike came back off the post, denying Boro’s superb 5,000-strong travelling support a late consolation.
Arsenal: Szczesny, Chambers, Gabriel, Koscielny, Gibbs, Flamini, Cazorla, Sanchez (Rosicky 72), Ozil, Welbeck (Walcott 72), Giroud (Akpom 83). Unused substitutes: Mertesacker, Monreal, Martinez, Coquelin.
Middlesbrough: Mejias, Fredericks, Omeruo, Gibson, Friend, Clayton, Leadbitter, Bamford (Reach 54), Tomlin (Vossen 54), Adomah, Garcia. Unused substitutes: Ripley, Husband, Whitehead, Nsue, Woodgate.
Referee: Mike Dean (Wirral).