For the Premier League leaders, the result also constituted a 10th straight win in all competitions and an eighth consecutive clean sheet.

They have now scored 11 goals and conceded none in the Champions League so far as they maintained their perfect start.

"The most pleasing thing probably is not the record, it's the mindset of the players, they are talking there about how we can still do better," said Arsenal manager Mikel Arteta.

The match also saw a moment of history as Arsenal's Max Dowman became the youngest-ever player in a Champions League game aged just 15 years and 308 days when he came onto the pitch in the 73rd minute.

Stand-in captain Bukayo Saka opened the scoring from the penalty spot on 32 minutes after Slavia captain Lukas Provod had handled the ball in the box clearing a corner.

Merino made it 2-0 from a quick breakaway 30 seconds into the second half as he volleyed home at the near post after Leandro Trossard's superb pass found him unmarked in the Slavia box.

The Spaniard then beat Slavia goalkeeper Jakub Markovic with a header from Declan Rice's cross on 68 minutes.

"I was really happy with the win, four in a row without conceding a goal," said Arteta.

"Very short sequences of play, a lot of fouls, a lot of restarts, very difficult to get any fluency in the match but if we were patient and emotionally controlled, we were going to have our chances," he added.

"At the end, it looked comfortable, but I don't think it was a comfortable match at all," said Arteta.

- 'An amazing feeling' -

He lavished praise on his compatriot Merino, who was one of four changes Arteta made from Arsenal's 2-0 league win at Burnley on Saturday.

Merino has "really good timing and capacity to finish in the box, especially one touch", said Arteta, hailing the striker's "mindset and versatility".

"And then it's obviously his quality, his willingness to learn and practise every day," he added.

Merino told UEFA.com scoring twice was "an amazing feeling".

"It is also thanks to my team-mates, who gave me two amazing passes and supported me through the whole game. I am very, very happy."

The game got off to an eventful start as Gabriel Magalhaes blasted wide from outside the box and Provod followed suit at the other end inside the opening two minutes.

But any effort by Slavia to get close to the Arsenal goal stumbled on the Gunners' rock-solid defence, and the reigning Czech champions failed to produce a single shot on target during the match.

Arsenal were soon on the front foot, dominating possession and creating chances despite missing injured strikers Viktor Gyokeres, Kai Havertz and Gabriel Martinelli.

Saka alone had three shots on goal within eight minutes midway through the first half but was denied by Slavia's Markovic each time.

The goalkeeper also then stopped the Arsenal captain's low shot from inside the box on 60 minutes.

The loss leaves Slavia, the Czech top-flight leaders, with two points from four games in the Champions League.