WALES do not need much more motivation to beat Fiji than the knowledge that a win would secure them a World Cup quarter-final against South Africa.

But Martyn Williams admits victory on Saturday would be extra-special given captain Gareth Thomas will be winning his 100th Test cap.

Thomas will become the first Welshman to achieve the feat and he joins an exclusive club of just eight international players to have played 100 Tests.

The ton-up club is headed by Australia scrum-half George Gregan, who has a world record 137 caps, and includes Fabien Pelous, Jason Leonard, Phillippe Sella, Stephen Larkham, David Campese and Alessandro Troncon.

Williams said: "You don't want to let Alfie down. It is a huge occasion for him. To become the first Welsh player to do it is an unbelievable achievement.

"He made his debut in 1995 so to play 12 years of international rugby takes some doing. He has more or less been in the side constantly since.

"It does add a bit of an edge to it - but for him the game is bigger than him winning 100 caps.

"It would just finish the day off nicely for him if we could win.'' Less than two weeks ago, Thomas was left fearing he could be stuck on 99 forever after suffering rib cartilage damage in Wales' defeat to Australia that threatened to rule him out of the tournament.

But he has made a remarkable recovery and replaces Kevin Morgan at full-back for Wales' World Cup eliminator.

"It is a huge achievement for him.

"No-one deserves it more than him,'' said Williams. "To finish on 99 caps would have been disastrous.'' Thomas took a bow after being greeted by a round of applause from his team-mates at the official team announcement yesterday.

His Test debut came at the 1995 World Cup in the last days of amateur rugby and he marked the occasion with a hat-trick of tries against Japan.

Thomas developed a reputation for being a maverick in his early years, but emerged under Steve Hansen's reign as one of Wales' senior players.

Thomas was appointed Wales captain by Mike Ruddock and led the side into the 2005 Grand Slam. Later that year he replaced injured Brian O'Driscoll as the British Lions captain.

Thomas has never been to far away from controversy.

In 2006 he suffered a "mini-stroke'' following an infamous appearance on BBC Wales' Scrum V to deny the players had forced Ruddock out of the job.

New coach Gareth Jenkins initially appointed Stephen Jones as his captain, but turned to Thomas for the summer tour of Australia and for the World Cup.

Jenkins believes Thomas is playing better now, at his fourth World Cup, than at any time over the last 12 years.

"Gareth's importance to this team cannot be understated,'' said Jenkins.

"He's a really special guy and he's earned the right to get where he is. He's been a fantastic professional all through his career. He's matured and grown as he's got older.

"This 100 caps is hugely deserved and I'm proud really to have given him the chance to accept the honour. His stature and composure on the rugby field will be invaluable to us in a game that could offer us such high rewards.

"We are within touching distance of a place in the Rugby World Cup quarter-finals.'' Thomas will lead out a side featuring seven changes from the 72-18 win over Japan, including a surprise start in the second row for Ian Evans at the expense of Ian Gough after playing just 20 minutes of rugby since December because of a shoulder operation.