The 96-cap veteran had to contend with a place on the bench during the 25-16 defeat to Australia.
But with Sam Warburton ruled out, Williams is expected to reclaim his starting spot as the countdown to 100 continues.
“I’m gutted for Sam. He went really well on Saturday and is really unfortunate to pick up a calf injury that rules him out.
“We push each other in training and get on really well. I’m just disappointed for him.
“Of course I’m aware of how close I am to 100. Any player who gets this far would be lying if they say they don’t realise how close they are.
“Mark Davies, our physio, says to me I’m like a batsman in the nineties at the moment, nervously twitching away. But, fingers crossed, I’ll get there.
“It’s such a nice milestone to get. Only Alfie (Gareth Thomas) has ever done it for Wales. It’s obviously in the back of my mind. But I don’t think you can let that be the whole focus of things either.
“I’ve been around long enough to realise you can’t look too far ahead. I’ll just concentrate on this one and hopefully the rest will look after themselves.”
And next up for Williams is the familiar opposition of the Springboks on Saturday.
“First and foremost we are disappointed that we lost to Australia. When you look back with the amount of ball we had we should have caused more problems,” continued Williams.
“They had the benefit of already having played a game and hopefully we can push on and be a bit more creative against the Springboks.
“We need a win and it’s another chance to claim a Tri-Nations scalp.
“We’ve got so close over the last couple of years and it seems to have been the same old story after every game, of little chances that we haven’t taken. We’ve got to make sure this week we are not talking about that after the game.
“They’re a very tough side, but as strong as they are up front you can’t underestimate their backs. It will be a tough challenge for us but we have to focus on ourselves.
“We’re all quite familiar with them and have played them a lot in the last three or four years. We know their strengths and they know ours.”
After coming last in the Tri Nations many believe the Springboks present Wales with the best chance of a big scalp.
And although Williams believes the gap between the Northern and Southern Hemispheres has closed he insists the Springboks will be as tough as ever.
“You never play a poor South African side and Saturday’s game will be as tough as any.
“There is nowhere near the gap that there used to be. When I started we would be happy to keep the score below 30. Now we are disappointed to lose and expectations are high.
“You can’t write South Africa off. People say they had a poor Tri Nations but they lost one game by a point or two and another in the last minute.
“They’re still a great side and the current World Champions. The core of their side is still made up of World Cup winners and they know what it takes to win.
“Australia was a great chance, we didn’t take it and we have to make the most of the chances we get against a great Springboks side.”