Alastair Cook believes the recalled Jonny Bairstow is "unrecognisable" as a batsman from the last time he played Test cricket.
England have sought to address the frailties exposed by Mitchell Johnson and his Australia pace colleagues at Lord's, by replacing Gary Ballance with his Yorkshire team-mate Bairstow and pushing the out-of-form Ian Bell up to number three.
Cook is optimistic that the changes will have the desired effect, with the Ashes level at 1-1 and three to play, in the third Investec Test at Edgbaston which starts on Wednesday.
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Bairstow is back for his 15th cap, 18 months after the last in Sydney at the end of England's whitewash 2013-14 series defeat, thanks to his prolific run-making in the LV= County Championship.
Cook has seen none of that first hand, but was impressed already by what he did witness from Bairstow batting against England when they mixed up the teams to ensure a competitive contest in St Kitts at the start of their tour of the Caribbean in April.
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"He got a brilliant 90 ... and was unrecognisable from where he was last time," said the England captain.
"Players are allowed to improve ... he couldn't be in a better place, seems really relaxed and I know he can't wait to play."
Bairstow has hit five Division One hundreds, including a career-best double, for Yorkshire this season.
Cook added: "Congratulations to Jonny - he's knocked the door down with his weight of runs for Yorkshire, averaging over 100 for the side that's top of the league.
"That's fantastic cricket at any level, let alone the first division with Yorkshire."
Bell, meanwhile, must rise to a different challenge as he seeks a return to the form which has helped him rack up 22 centuries in his 112 Tests.
"You're always playing for your place," said Cook.
"In any international team, there's a huge pool of talent - good players who want to take your place. When you go through a tough time you start looking over your shoulder.
"Whether you have played 100 games or 10, people want your place. They want to play for England, because that is the pinnacle of this sport."
Australia captain Michael Clarke has great respect for the talents of both Bairstow and Bell.
He said of the Yorkshireman: "He's a really good player, an attacking player, and he's performed well in county cricket this year.
"He'll be full of confidence, but I would hope the attack he's about to face is a little bit different to what he's faced in county cricket."
As for Bell, he added: "He is a great fella and a hell of a player who has been extremely successful for England over a long period of time.
"Whether he makes runs in this series, I'm sure it's not the end of his career."