Halfpenny added his second kick to trim South Africa's lead to 12-6 after 24 minutes.
Leigh Halfpenny may be set for a cap, but Tom Shanklin's spot may be at risk.
Eifion Roberts (Sale), Dan Biggar (Ospreys), Martin Roberts (Scarlets), Powell and Halfpenny were called up.
There were a number of forwards defending out wide when Leigh Halfpenny scored Wales' try.
Halfpenny's arrival in South Africa takes the tour party back to 37 players, as originally announced.
Halfpenny has just been called up to the Wales squad for next month's autumn test series.
Two sparkling Leigh Halfpenny tries helped the Blues take an early 17-0 lead at Twickenham.
Jean Halfpenny, 89, died in May 2010 at Orchid View care home in Copthorne.
Cardiff sacrificed Leigh Halfpenny for Richard Mustoe, before Edinburgh lost Kyle Traynor, with Gavin Kerr coming on.
Ceri Sweeney and a Leigh Halfpenny brace brought up the bonus point with just over half-an-hour played.
Other wing options for Wales include Leigh Halfpenny, Tom James, Jamie Roberts, Morgan Stoddart and Richard Fussell.
Halfpenny also played against France but missed out for the final two games against Italy and Ireland.
Lee Byrne came close while Leigh Halfpenny had a great first cap and deserves to keep his place.
The fullbacks are Leigh Halfpenny, Stuart Hogg, Rob Kearney, Tommy Bowe, Alex Cuthbert, Sean Maitland and George North.
Wales wing Halfpenny opened the scoring at the Liberty Stadium with an early penalty, but their lead was short-lived.
An excellent Leigh Halfpenny try plus another from Sam Hobbs gave Wales hope.
Tom Prydie switches to the left wing with Leigh Halfpenny on the right.
His Blues team-mate Leigh Halfpenny thought he had added a second minutes later but his try was ruled out.
Skipper Ryan Jones, Leigh Halfpenny and Tom Shanklin are the three retained after the 20-15 loss to South Africa.
Blues pair Leigh Halfpenny, 19, and Andy Powell, 27, will win first caps.
The arrest relates to the death of Jean Halfpenny, 89, in 2010, at Orchid View care home in Copthorne.
BBC: Orchid View Care Home neglect inquiry: Man held over death
Away with the Wales squad are Bradley Davies, Richie Rees, Tom James, Leigh Halfpenny, Jamie Roberts and Tom Shanklin.
Leigh Halfpenny may not be considered as he requires an operation, with injury almost certain to rule out Mark Jones.
Teenage Blues wing Leigh Halfpenny claimed a stunning first-half brace while Gareth Thomas and fly-half Nicky Robinson also touched down.
Halfpenny has been undergoing intensive treatment with the Cardiff Blues medics but they are now satisfied with his fitness levels.
The fly-half took a quick throw to himself from Halfpenny's long touch-finder and spotted Fernandez Lobbe lurking on the left.
Moments after Biggar missed the conversion, replacement Leigh Halfpenny, on for the injured Blair, almost replied instantly for the hosts.
Jamie Roberts, Leigh Halfpenny, Dan Evans, Martyn Thomas and Jason Tovey are other potential candidates, with Morgan Stoddart still injured.
Halfpenny will try to enhance his reputation by following the example set by Wales' Shane Williams and New Zealand's Sitiveni Sivivatu.
With Wales' 20-year-old wing Leigh Halfpenny yet to join the tour, Earls, 21, is currently the youngest player in the squad.
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