Captain Sam Warburton and centre Jamie Roberts believe Wales will have a fitness edge over England in their Millennium Stadium rematch on Saturday.
But the duo concede Wales' defence must improve following their 23-19 World Cup warm-up defeat by England at Twickenham.
"We were certainly the fitter team come the end of the match," said Cardiff Blues centre Roberts.
Flanker Warburton said: "Our first-up tackling has to improve."
Wales scored three tries to two, through wings George North, with a brace, and Shane Williams, with number eight James Haskell and centre Manu Tuilagi replying for England.
The visitors lost full-back Morgan Stoddart to a broken leg that rules him out of the World Cup.
But Wales have described the calf strain that forced fly-half Stephen Jones to miss out on a record 101st cap as "minor".
However, Wales have not yet revealed whether or not the Scarlets fly-half will be fit for consideration for the rematch in Cardiff.
After leading his side from 20-7 down at one point, Roberts' Blues team-mate Warburton said: "We were pretty strong in the last 20 minutes. I think England were hanging on.
"But it was pleasing. We've always struggled to score tries in the Six Nations and to score three tries - all coming from our wingers - shows our attack is working.
"There was a couple of first-up tackles which we missed, which allowed them to have line-breaks and then you're on the back foot from there.
"And the one that stands out was when Tuilagi went through.
"It was just so disappointing to finish so strong and come away without a win.
"Hopefully, next week it means we'll have to start a bit better and back our fitness levels a bit more as we know we can go the full 80."
Roberts said: "To come back from where we did and almost clinch it showed we are a strong side.
"But we are disappointed to have conceded two soft tries. Haskell's try off the back of a scrum, maybe we got our defensive set-up wrong there.
"And it was a good line from Manu [Tuilagi] for his try, but our defence was quite weak under our posts, so two soft tries were conceded, really."
Wales' pre-World Cup fixtures ends with a Millennium Stadium clash against Argentina on Saturday, 20 August.
Two days later Gatland announces his 30-strong squad to travel to his homeland for the tournament, where they face South Africa, Fiji, Samoa and Namibia at the group stage.
Wales' preliminary World Cup squad
Forwards: Scott Andrews, Gethin Jenkins (Blues), Lloyd Burns (Dragons), Huw Bennett, Ryan Bevington, Adam Jones, Paul James (Ospreys), Ken Owens, Matthew Rees (Scarlets), Craig Mitchell (Exeter), Bradley Davies, Sam Warburton, Martyn Williams (Blues), Luke Charteris, Danny Lydiate, Toby Faletau (Dragons), Ryan Jones, Alun Wyn Jones, Jonathan Thomas, Justin Tipuric (Ospreys), Josh Turnbull, (Scarlets),Gareth Delve (Melbourne Rebels), Andy Powell (Sale Sharks).
Backs: Michael Phillips (Bayonne), Lloyd Williams (Blues), Tavis Knoyle (Scarlets), Jamie Roberts (Blues), James Hook (Perpignan), Jonathan Davies, Stephen Jones, Rhys Priestland, Scott Williams (Scarlets) Gavin Henson (unattached), Leigh Halfpenny (Blues), Lee Byrne (Clermont Auvergne), Aled Brew (Dragons), Shane Williams (Ospreys), George North (Scarlets).