Despite being stunned by a lower-ranked Sri Lanka side in their last warm-up game, England captain Heather Knight has backed her team's "massive preparations", making it clear she is not worried about the mental make-up of her side heading into their T20 World Cup opener against South Africa on Sunday.

The runners-up in the 2018 edition of the tournament, and holders of the 50-over World Cup, England suffered an eyebrow-raising 10-wicket loss in that practice match in Adelaide. Knight conceded they were blindsided by the pace of the Sri Lanka spinners and a superlative all-round performance from opposition captain Chamari Atapattu, who took 3 for 21 and made 78 not-out after England opted to bat.

"It was a good leveller, to be honest," Knight said of the shock loss. "We were well off our best but Sri Lanka played really brilliantly. Their spinners bowled a lot quicker than we are used to. We probably didn't adapt very quickly and then Atapattu just played a brilliant innings, and that can happen in T20 cricket.

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"It's that kind of a game; if you are not completely on it, you could bite your nails a little bit. Credit to them, they played brilliantly, but I am not too worried. We've had massive preparations, we've played really good cricket and we've been learning along the way as well, so it's about how well we start [the tournament]."

The defeat to Sri Lanka came after a comfortable win over New Zealand in England's first practice match two days prior, led by Knight's unbeaten 45 and a three-for from Katherine Brunt. That victory hauled the team back into winning ways after an up-and-down performance in a closely contested tri-series last month saw them finish last on net run rate, with India and eventual winners Australia reaching the final.

Despite their failure to progress, a Super Over win against Australia and then a reassuring four-wicket victory against India in Melbourne showed just why England remain strong contenders to make the T20 World Cup knockouts for the fifth tournament running.

"There were a lot of learnings," Knight said, looking back on the tri-nation series. "I feel we [have] really built up as a team since the start of that tri-series. The bowlers in particular have gotten used to the conditions and are really firing, which has been pleasing from where we probably were at the start of the tri-series. From where we were to where we have got to has been quite brilliant.

"And the close games, there were a few really close games which we were pleased with to get over the line against some of the best teams in the world. We have continued to improve: we have had some success and some low levels as well, which isn't the worst thing."

Much of the team's preparations in the lead-up to the World Cup, Knight said, have been focused on the responding to the call to "step up more" from newly appointed head coach Lisa Keightley. Now they have worked together for a while, Knight believes Keightley "goes about her business in a more relaxed manner".

"She is quite chilled and wants players to take aim, which is exactly what we have wanted to do following the Ashes as well," Knight said. "We want to step up more as players, make more of an impact on how we want to do things. The players have responded well to that. I have enjoyed that. I have always enjoyed taking a leading role, so I guess I've taken a bit of a lead since the Ashes. Myself and Lisa, we share a good relationship and hopefully we can bring success.

"I've really enjoyed working with her. I know her very well from her stint in England [with the Women's Academy]. She is more of a quiet coach. She likes to go about her business in the background, build one-to-one relationships. As a squad, even before Lisa came in we did a lot of work [together]. We have had the chance to assess what we were about as a side, how we want to do things, how we want to go forward, things we want to keep going and things we want to change a little bit."

With a return on the cards for allrounder Nat Sciver, who missed the warm-ups due to a niggle, Knight underscored that England, currently ranked No. 2 in T20Is, are well poised to put up an impressive show on Sunday at the WACA, where the same pitch will be used as the one for Saturday's low-scoring double-headers.

Much of Knight's optimism stems from the prior experience of players like Sciver and Amy Jones, who are part of the WBBL franchise Perth Scorchers, and Keightley, formerly coach of the Scorchers and Western Australia.

"A lot of our players have played at the WACA, played for the Scorchers and then you've got Lisa, who used to coach there," Knight said. "So, she knows the conditions inside out. She has spoken a lot in terms of how to be successful at the WACA.

"They don't actually play a lot of games under lights there, because of the time difference. So, that's probably going to be slightly different. We are going to have to adapt to that and make sure we communicate as a side very clearly when we are around the pitch.

"We were training under lights yesterday, so it skidded on a little bit more than it probably did previously. It was a little bit tennis-bally when it was dark. We have prepared for it in our individual skillsets."