The Pompey Academy forward spent a brief spell on the sidelines with concussion earlier in the year.
After taking a couple of games to get back up to speed, Lethbridge has recaptured all of his prowess in the final third.
Last weekend, the Gosport talent’s hat-trick inspired the young Blues’ fightback at Bristol Rovers in Merit League One.
Despite being 3-0 down at half-time, Pompey battled back to deliver an unlikely 4-3 victory against the Pirates.
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And Kelly praised Lethbridge, who also scored in yesterday’s loss to Southend, for putting the work in on the training ground.
‘He had concussion for a few weeks and took a while to get back,’ the Blues’ youth chief said.
‘It’s one of them things but Bradley is starting to find his rhythm again.
‘He is getting his work done on the training ground to sharpen himself up and he’s starting to score goals again. That’s really good for him.
‘It’s nice to see Bradley sharpen up now, getting a hat-trick. He’s starting to again find his form in front of goal and things are starting to flow.’
The academy’s current make-up is primarily made up of first-year apprentices and schoolboys.
The majority of the second-year scholars are out on work-experience loans gaining experience.
Meanwhile, Dan Smith is currently involved in Kenny Jackett’s first-team set-up.
Kelly revealed Pompey are coming up against sides with greater experience and age.
And he believes the first years have taken on the mantle well.
Kelly added: ‘It’s an interesting time of the year for the first years.
‘A lot of the second years are out on loan.
‘The first years are really stepping it up. We’ve then got some of the under-16s who are joining them.
‘There’s a nice balance going on everywhere and it’s a really good challenge at the moment.
‘I’m quite enjoying the challenge which all individuals are getting.
‘That is good and it’s the right place for the boys to be.
‘Against Bristol Rovers, Matt Mayes was the only second year as Matt Casey was injured.
‘You’ve then got Dan Smith with the first team, Jordan Brooks is over at Gosport, while Jack Chandler and Jack Collins are at Alton and Littlehampton.
‘They’re all getting their senior experience and everyone across the board is getting their challenge – that is good for them.
‘We’re coming up against teams who are older than us but we’re not bothered – it’s about challenging the boys.’