Clarke and Smith scored centuries to honour the memory of fallen team-mate Phillip Hughes and leave the Australians on 517 for seven after a rain-hit second day of the Adelaide Test.
Clarke needed painkilling injections for a chronic back injury but scored 128, while Smith was unconquered on 162 at the close.
Smith, who is seen as a future captain, said Clarke was "mentally drained" after a heart-wrenching few weeks over the death of their close friend Hughes, fatally struck by a bouncer in a domestic game.
Clarke comforted Hughes's family, delivered a tribute at his funeral and acted as a pallbearer.
"He has done amazing over the last couple of weeks," Smith told reporters.
"It has been tough for all of us but he spent the whole time by Hughesy's family's side.
"Just the strength and courage he has shown through those times was unbelievable.
"He must be mentally drained coming into this game but the way he played speaks the world of that guy. He came out here and tried to do something for Hughesy and he certainly did that."
Clarke returned to the crease at the outset of day two after retiring hurt on 60 with back trouble on Tuesday's opening day.
"He was pretty keen to get out there this morning. He had a good hit this morning and he just came out and played beautifully," Smith said.
"A few shots hurt him but he got himself into as many good positions as he could and manipulated the field a little bit as well. He played beautifully under the circumstances."
Smith, 25, marked his own century by moving away from the wicket and pointing symbolically towards the '408' -- Hughes's Test cap number -- painted on the playing surface.
He said Hughes's death had been a shattering experience for the team.
"The last couple of weeks have been very tough for every one of us," he said.
"I thought I'd be able to get over it pretty quick after the funeral and try to move on and go out there and do something I love to do.
"I know that's what Hughesy would have wanted, all of us to be out here doing the job and he was with me, Pup (Clarke) and Warner all the way this innings.
"We're all good mates with Hughesy, us three, so I was sort of hoping all three of us would get runs."
Smith took 23 Test innings to reach his maiden century. He now has five Test tons, four of them in his past 15 innings.
"I'm not sure if it's my best innings. I think my hundred at Centurion against South Africa in those conditions would probably be my best one so far in my book, but every hundred's nice and hopefully I've got a few more this summer," he said.
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