Mikel Arteta challenged his Arsenal squad to bare their teeth and prove they have the tools to fight for the title despite stomaching a significant injury to Kai Havertz. For 80 minutes it seemed fears of being blunt in attack would be founded in a frustrating stalemate at struggling Leicester but then the excellent Ethan Nwaneri dinked a feathery cross into the box and the substitute Mikel Merino, unmarked between Wout Faes and Woyo Coulibaly six yards out, twisted his head to power in the first of his two goals. Merino, who replaced the ineffective Raheem Sterling, sealed victory with his second with three minutes of normal time to play.

Related: Keown apologises to Van Nistelrooy for infamous Old Trafford ‘shenanigans’

Arteta began with Leandro Trossard as a false 9, Sterling to his left and Nwaneri to his right in a three-pronged attack but until Merino’s header the Arsenal manager must have been wondering how else to penetrate Leicester, now without a clean sheet in 21 matches in all competitions. This was the first Premier League game in which Arsenal began without any of Bukayo Saka, Gabriel Martinelli, Gabriel Jesus or Havertz, who is out for the season with a hamstring injury, for almost four years. But Merino ensured Arsenal cut the gap to Liverpool, the leaders who host Wolves on Sunday, to four points for at least 24 hours.

It could, as Arteta acknowledged, have been a different picture had another Arsenal teenager, Myles Lewis-Skelly, not made a magnificent intervention. Eight minutes before Merino’s header, Arsenal surrendered possession on halfway and Jordan Ayew sent a ball rolling invitingly across the face of goal. Bobby De Cordova-Reid was lurking at the back post for a tap-in but the 18-year-old Lewis-Skelly spied the danger and flicked his right boot at the ball to make a goal-saving interception and clear for a corner. It was arguably the moment of the match given how the game was poised at that point. A magic touch, as Arteta put it.

The game had been approaching the point where William Saliba, a striker at boyhood club Bondy, where he was coached by Kylian Mbappé’s father, must have thought about piling forward from centre-back. Sterling and Trossard fluffed half-chances. Martin Ødegaard slipped in Nwaneri but, on this occasion, the teenager ran out of road. When Arteta withdrew Sterling, it was down to Merino to operate as a forward. “It’s the first time that I’ve played as a striker,” the Spain midfielder said. “It’s a good day to score because I forgot to give my wife a Valentine’s Day present, so I think she’ll appreciate this more than a rose or some chocolates.”

It was inevitable that Nwaneri was involved in Arsenal’s significant first goal. The twinkling 17-year-old was Arsenal’s most dangerous player, full of juice, deft in possession, adept off both feet. Just after the hour the teenager’s shot skimmed the top of the Leicester crossbar and with time ticking he cracked a shot against a post, via the fingertips of Mads Hermansen.

“Every sign that he’s given us is: ‘Let me go for it, let me go,’” Arteta said of Nwaneri. “When a player is giving you all those signs, you should not stop it. You have to play with that freedom, with that creativity, with that confidence he’s playing with, and the players believe in him. He’s a massive threat, a massive talent and deserves to play.”

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The Leicester goalkeeper tried to rouse his teammates after conceding but the game was soon over, Merino capping a slick counterattack. The substitute Riccardo Calafiori brought the ball forward and passed the baton to Trossard, who curled a ball towards the far post where Merino did the rest. “He’s a good threat because he can smell danger,” Arteta said.

For Ruud van Nistelrooy, it was another agonising brush with Arsenal, though before the match Martin Keown did at least apologise for “the shenanigans that went on back in the day”. On the day Leicester’s supporters staged a series of protests against the board, starting at the Local Hero pub, half a mile from the stadium, a couple of home-reared talents helped Arsenal stay in the hunt at the top. “With everything that happened in the last few days, it was important to show how much we want it, we’re really going to go for it and that we believe in what we have,” Arteta said.