Antonin Kinsky has bred confidence in his new Tottenham teammates and liberated them, according to the manager, Ange Postecoglou, who is ready to pitch him into another huge challenge on Wednesday night – the north London derby at Arsenal.

It has been a whirlwind period for the 21-year-old goalkeeper since his arrival from Slavia Prague on the Sunday before last; the £12.5m fee made it one of the most expensive transfers from the Czech league.

Related: ‘It’d be almost impossible’: Postecoglou defends the scrapping of FA Cup replays

With the regular Spurs No 1, Guglielmo Vicario, out with a fractured ankle, Postecoglou put Kinsky into the lineup for the Carabao Cup semi-final first leg at home against Liverpool last Wednesday. Everybody knew how it would have been portrayed if Kinsky made a mistake but he starred in the 1-0 win, making a couple of fine saves, and was largely assured with his distribution.

Then came a different game in the FA Cup on Sunday at non-league Tamworth, who brought a no-frills aerial approach on set pieces, including long throws. Kinsky stood firm in the 3-0 extra-time victory to become the first Spurs goalkeeper for more than 100 years to keep clean sheets in his first two matches. Postecoglou said he could talk up Kinsky’s technical ability but what had really impressed him was his mindset.

“It’s more to do with being prepared to embrace the challenge,” Postecoglou said. “It’s not easy going to a place like Tamworth and they’re throwing balls literally under the crossbar and you’ve got about 20 bodies around you. It’s more about mindset and tackling that, and he didn’t shy away from it.

“It does give some comfort to the players around him if they see he’s handling it well. It means they can focus on their own job and be a lot more clear-headed. When he came out and dealt with the first two and caught them, the players around saw that he’s got this. If he didn’t and there was uncertainty, it tends to filter through the whole team.”

The atmosphere at Tamworth was hostile, with Postecoglou receiving terrible abuse from the fans behind his bench. “The stuff I heard was pretty vile and detestable, and getting things thrown at me … not a great experience,” he said. “We’re kind of expected to be the bigger person, but I would love to have turned around and not been the bigger person in that moment.”

Kinksy may reflect that the Tamworth experience will prepare him for what Arsenal will seek to do on set pieces – get men in his six-yard box; physically unsettle him. When Arsenal won 1-0 at the Tottenham Hotspur Stadium in the fourth game of the Premier League season, Gabriel Magalhães’s goal came from a corner and it continued a trend.

Spurs had conceded from a set piece in their previous match – the defeat at Newcastle – and were breached 16 times from set pieces in the league last season; only three clubs conceded more. Since Gabriel’s goal, though, they have let in only four from set pieces. As an aside, Spurs have conceded the fewest goals in the division away from home – nine.

“It’s the evolution of the team,” Postecoglou said. “Last year, people were pretty simplistic in their outlook when I spoke about set pieces, that I didn’t care about set pieces and we didn’t have a set-pieces coach so we didn’t work on them. We haven’t put more emphasis on it. We’ve changed a few things around with the way we’re defending and it’s working really well for us this season.

“When we played Arsenal at our place, they scored a good goal and that was the difference. They’ve done that to a lot of teams but for the most part we handled the set pieces well and we will have to again. Declan Rice delivers a great corner and they’ve got some big guys.”

Postecoglou spoke about how the in-form striker Dominic Solanke, who joined last summer, had “exceeded” what he was hoping for. But the manager is happy that Richarlison is poised to return after two and a half months out to reduce the load on Solanke. Spurs are desperate for a positive result after winning once in eight league matches and losing five, slipping to 13th place.