Adam Gilchrist isn't sure he belongs among the top tier of Australian Test batsmen despite joining elite company with his remarkable double century against South Africa at the Wanderers.

Gilchrist was today still absorbing his unbeaten 204, which again propelled him past names like Greg Chappell, Neil Harvey, Allan Border and Steve Waugh on Australia's list of Test batting averages.

Of the batsmen to play more than 10 Tests, Gilchrist's average of 57.30 is behind only Don Bradman (99.94) and Sid Barnes (63.06), and just 0.05 ahead of Damien Martyn, his demolition partner yesterday.

That Martyn's excellent 133, in a record-breaking stand of 317 for the sixth wicket, was almost lost beneath Gilchrist's onslaught on the second day said plenty about one of the most ruthless innings ever seen in Test matches.

At 212 balls, it was the fastest double century recorded in Tests, eight balls quicker than Ian Botham's knock against India at The Oval in 1982.

His eight sixes, including two out of the Wanderers grounds, were the most by an Australian in one innings and his stand with Martyn was only the second sixth-wicket partnership to surpass 300 runs.

And all this from a wicketkeeper who didn't play his first Test until nine days before his 28th birthday.

But the humble Gilchrist typically wanted to play down his Test record even though just nine batsmen from all countries have averaged better than him at the same stage of their careers.

"I don't think you can focus too much on it," Gilchrist said.

"I have been up this high before in the averages and seen 10 runs get wiped off in one series. Averages are things you look at when you are finished but it is hard to gauge at the moment.

"I think we are the beneficiaries of some great work by the top order which gives us the chance to play our natural games."

Gilchrist's friends wouldn't expect him to say anything different but it was hard even for him to downplay the nature of his fifth Test century.

The left-hander was cautious after coming in against the second new ball, taking 89 balls to reach his half-century, but he wiped the next 50 off in just 32 deliveries as South Africa's thin layer of confidence was shattered.

Gilchrist, batting at No.7, doesn't often face a new ball or the responsibility of performing each time he bats, but the more recognised batsmen don't have the burden of wicketkeeping.

Moments after Gilchrist reached his double century, captain Steve Waugh declared his first innings closed at 7-652 and South Africa was paddling at 4-111 in reply when the long second day ended under lights.

"I haven't had a lot of time to sit back and reflect but obviously it is a fantastic personal milestone," Gilchrist said.

"It was an amazing day and something that will always be memorable. We will have to wait and see when I finish my career where it rates."

It was an emotional innings for Gilchrist, who raised both arms to his teammates and then crouched to the ground after reaching his century.

The 30-year-old has endured a testing summer, pulling out of a one-day international last month to be with wife Mel and baby son Harrison, who wasn't well in his first weeks.

Harrison has since recovered but Gilchrist admitted it was tough to be away from his family.

"We are all under pressure and miss our family and partners. It has been a full-on summer in that regard with Harrison being born," he said.

"Everyone knows I missed a game to be with Mel and Harrison during a tough period.

"You are a long time on the road and miss friends and family. It is nice to know you have the support of your team-mates who are a fantastic bunch of guys."

© 2002 AAP