Lions assistant and Wales defence coach Shaun Edwards has underlined Shane Williams' match-winning ability.
The 2008 world player of the year was named in the Lions squad despite a disappointing RBS 6 Nations campaign when he failed to hit last season's heights.
Lions forwards coach Warren Gatland revealed it had been a close call whether Williams made the final cut, despite his Welsh record of 46 Test tries.
"He is a player who has done it in the white-hot environment of Test rugby," said Edwards.
"With the amount of attention that Shane gets in Wales, we can take him away and concentrate on his rugby.
"Shane Williams can be a thorn in South Africa's side."
Edwards also revealed 20-year-old Leigh Halfpenny's electric display for the Blues in last weekend's 50-12 rout of Gloucester at Twickenham - he scored two tries - underpinned his selection.
"His performance last Saturday was exceptional," added Edwards. "He also played extremely well in the autumn Tests."
Acclaiming his team's Lions representation, Blues head coach David Young said: "We are delighted for all the players from our squad that have been selected but also feel for the ones that didn't make it.
And Welsh Rugby Union chairman David Pickering said: "Rugby in Wales is in a good place - we are going from strength to strength and intend to continue in that vein.
"The Irish were deserved and impressive Grand Slam champions in the end and they rightly make up a large proportion of the Lions tour party but Wales has not been overlooked.
"The performances of the Blues in the EDF Energy Cup, and so far in the Heineken Cup, have caught the eye and it is no surprise that six players from that region have been selected.
"Teams can win one-off games in World Cups and other competitions but to come out on top in a series like this when a squad is gathered together from a number of nations is against all the odds.
"But the magic of the Lions is that it's possible and that is what makes the British and Irish Lions tours so very special."