When Arsenal dismissed their manager of three years, Pedro Martínez Losa, four weeks into the new season it was a surprise. But the quick action to remedy a stuttering start was broadly welcomed and the club’s replacement, equally surprisingly, has worked wonders with a side leaking goals.

Arsenal had conceded eight times in three league games before Joe Montemurro’s arrival from Melbourne City and a promising squad with four European Championship winners was quickly falling behind the pack.

Since then they have let in eight goals in 12 league games, with an Ellen White hat-trick for Birmingham on Sunday responsible for a hefty chunk of that. They have turned a negative goal difference (-2) into +14, been on a nine-game unbeaten run which included eight clean sheets, won the Continental Cup and fought their way to Saturday’s FA Cup final against Chelsea at Wembley.

Montemurro has form when it comes to building solidity. The Australian’s Melbourne City side conceded five goals in their 14-match 2015-16 W-League season, scoring 42. They won every game, one on penalties.

At the heart of Montemurro’s new defence the 21-year-old Leah Williamson has thrived. Williamson, who made her senior debut for Arsenal in 2014, aged 17, puts the transformation down to the manager getting them to rewind. “Joe came in, he recognised those weaknesses in our play and he just took us back to basics,” she says. “No task is too little when you’re a defender. I think being a footballing team that likes to be on the ball, we were forgetting our defensive responsibilities, or maybe just putting them second to being on the ball.

“But obviously in a game of football you’re not on the ball the whole time and he just reminded us that as defenders our sole purpose is to defend. I know that sounds silly but it can be taken for granted sometimes. So he just took us back; basic movements, covering each other, working as a four and just tidying up. Once you strip it all down and go back to basics you realise how easy the changes are to make. And I think that’s how we were able to have such a rapid turnaround.”

There is also a fresh focus on pressing and putting themselves in the position to play the possession football they like. “We want to have the ball all the time, so as soon as anybody in the team turns it over we want to win it back as soon as possible and set them on their way again,” Williamson says.

“The transition from attack to defence is so dangerous – that’s what other teams in this league are good at. And we recognised that stopping the counter can save you 40 yards of running. It’s about managing the game for 90 minutes; the sooner you win it back the less running you’re doing. Little changes like that make a big difference in the end.”

Leah Williamson in action for Arsenal against Reading. She has been part of a defence that conceded eight goals in 12 league games. Photograph: David Price/Arsenal FC via Getty Images

The team’s backs-to-the-wall Continental Cup final victory against the holders, Manchester City, in March, won by Vivianne Miedema’s 33rd-minute goal, slotted through the legs of the goalkeeper, Ellie Roebuck, showed they can dig deep when needed. “It meant a lot to us, that game,” Williamson says. “One game and everyone views you differently. Before that we were a write-off.

“Being about to hold on to a 1-0 lead was something that we weren’t capable of before, for whatever reason. So it’s good to get that bit of confidence and then to know that, when we need to stick it out, which is not Arsenal’s style, it’s not what we like to do, we can.”

Montemurro’s maiden trophy came during an impressive run of eight clean sheets, which ended with a Fran Kirby goal in a 1-1 draw with Chelsea. “We were really gutted that we let in a goal against Chelsea because we were really proud of that record,” Williamson says. “It shows how your priorities change. Clean sheets go hand in hand with wins and points – there’s no secret there. We know we’ve got the talent to nick a goal.”

Saturday’s meeting with Chelsea is a repeat of the 2016 final, which Arsenal won 1-0. Williamson, who received her first England call-up last November, knows where the greatest threat will come from: “Fran Kirby is in unbelievable form – she has been all season. You can see when she doesn’t play, considering she scores a couple a game, they’re lacking. But they’ve been solid too. They’ve got a good defensive record and they haven’t lost a game yet in domestic competitions.”

Yet both clubs will be looking to put weekend disappointments behind them. Chelsea have just been humbled by a 5-1 aggregate defeat by Wolfsburg in the Champions League and Arsenal’s 3-0 loss to Birmingham ended any title ambitions they might have held.

Arsenal have not beaten Chelsea this season, and after Kirby’s double on the break in Chelsea’s semi-final against Manchester City, Williamson is wary: “We’ve got the talent going forward and the goals are coming from all over. We just need to trust in the process, don’t go searching for a goal and leave ourselves exposed. Chelsea’s second goal against City was one long ball and Fran got on the end of it. We just need to tighten up and reduce those spaces and try and limit that threat.”

Talking points

• There will not be an English representative in this season’s Champions League final after Lyon beat Manchester City 1-0 and Wolfsburg put two past Chelsea to set up a repeat of the 2012-13 and 2015-16 finals (one win apiece). The former City right-back Lucy Bronze struck a wonderful volley for Lyon, the only goal of the tie. Lyon’s midfielder Camille Abily, who has won 10 league titles and seven French cups, has announced she will retire at the end of the season. If Lyon beat Wolfsburg in Kiev it will be her fifth European title. Second-half goals from Wolfsburg’s Pernille Harder and Ewa Pajor ended any hopes of a Chelsea fightback.

Lyon celebrate after Lucy Bronze’s winner. Photograph: Romain Lafabregue/Icon Sport via Getty Images

• The Switzerland forward Ramona Bachmann has signed a new deal at Chelsea to 2021. Bachmann joined from Wolfsburg in January 2017 and has 10 goals in 33 appearances.

• Blackburn Rovers came from behind against Leicester City to win the WPL League Cup. After going a goal down to a Sophie Domingo strike, the captain, Lynda Shepherd, coolly converted a penalty to equalise. Ellie Cook then headed Rovers ahead before Saffron Jordan sealed the 3-1 win in their first final.