UPDATE: SRI Lanka has collapsed to be dismissed for 156 before tea in the Boxing Day Test in Melbourne.
In a reckless display on the game's biggest day of the year, the tourists have been in 43.4 overs.
The last seven wickets fell for 77 runs in a very unfortunate convergence of supposedly lucky numbers for the tourists.
After an indifferent morning, Johnson was on a hat-trick when he fired out Prasanna Jayawardene and Dhammika Prasad with a vicious display of short-pitched bowling, The Australian reports.
But Johnson has always mixed brilliance and carelessness, and so it was for the hat-trick ball - which was a no-ball.
Meanwhile Jackson Bird has taken two wickets on debut to show why the selectors were happy to wear the flak for blooding him at the expense of the rotated Mitchell Starc.
The Tasmanian has 2-22 from 12 overs (five maidens) to play more than a bit part in the recast Australian pace attack.
Halfway through Boxing Day Sri Lanka is 6-138, with Kumar Sangakkara on 57 and Rangana Herath on two.
Sangakkara has been unperturbed by the wickets tumbling all around him, playing with his usual sublime grace to hold the innings together.
Prasanna Jayawardene fell for 24 immediately after the afternoon drinks break. The Sri Lankan keeper gloved a steepling Johnson thunderbolt to Phil Hughes at third slip.
Prasad fell in the same manner, gloving the ball to Wade, for a golden duck.
Thilan Samaraweera (10, 38 balls) battled gamely for an hour - adding 42 with Sangakkara - before he skied Bird's third ball after lunch to Dave Warner at midwicket.
The Sri Lankan appeared hurried by the well-directed short delivery that struck high on the bat to balloon for the simplest of catches.
Angelo Matthews came in went quickly, his better than run a ball 15 not exactly what was called for in the circumstances.
The captain-in-waiting unfurled a cover drive at a wide, swinging, Peter Siddle ball, only for it to end in Mike Hussey's left claw at second slip.
The first session was a tale of two hours, Australia skittled the tourists' top order in the first before Sangakkara counterattacked in the second.
The Sri Lankan master received a standing ovation when he brought up his 10,000th Test run with a cracking cover-driven boundary off Johnson just before lunch.
Sangakkara took 15 runs from the first four balls of Johnson's seventh over - two straight driven fours, a boundary thrashed behind point and a flick through square leg for three.
Bird, controversially brought in to allow Mitchell Starc a rest, has bowled superbly on debut to go to lunch with 1-16 from eight overs against his name.
Dimuth Karunaratne entered the books as Bird's first Test wicket when the opener edged the paceman's 10th ball of the day to keeper Matthew Wade.
Taking the new ball from the Southern End, Bird immediately troubled the batsmen with his probing line and length delivered at brisk pace.
He forced the Sri Lankans to play at nearly every ball, although the breakthrough wicket came from a ball that Karunaratne might have left for the 'keeper.
The Blue-cum-Tasmanian delivered with the seam upright from close to the stumps and accordingly found sideways movement off the pitch as well as healthy outswing.
After both openers fell in the first half hour, skipper Mahela Jayawardene (three) dug in for 26 balls and 35 minutes before he feathered Peter Siddle (1-6) to Wade.
Michael Clarke used Siddle, his trump, sparingly, with the Victorian sending down only four overs for the session.
Johnson, however, has suffered at the hands of Sangakkara and will resume after the break with 1-44 from nine overs.
Thrust into an unfamiliar role as with-the-wind new ball bowler, Johnson immediately hurried Karunaratne with a 140 km/h yorker that the opener squirted fortuitously to fine leg.
Perhaps sensing Johnson felt uneasy in his new role, Tillakaratne Dilshan attacked the paceman from the outset, first punching a two through covers then flailing a boundary behind point.
But, in trying to swipe Johnson down the ground, Dilshan went too far and was bowled through the gate for seven.
The ball snaked back late but the ungainly shot was the last thing Sri Lanka needed in the first 30 minutes of such a crucial Test.
Dilshan was fortunate to survive a half shout for caught behind down the leg side from Johnson.
Replays showed the ball kissed two fingers of his glove on the way through to Wade.
The tourists had no hesitation in batting under bright blue skies on the biggest day of the cricket calendar.
Clarke said he would also have batted had he won the toss.
"The wicket looks great ... but we've got the ball in our hands now so we've got to start well," Clarke said.
Bird is debuting on the ground where he has excelled in taking 14 wickets at 12 in two Sheffield Shield matches.
He was presented with his Test cap as the 431st Australian Test player by Bill Lawry before play.
Bird took the new ball after Mitchell Starc was controversially rotated out of the side after playing just two Tests this summer.
Declaring himself "100 per cent" fit to play, Clarke made some pointed comments at the toss about criticisms of rotation policy that has relegated Starc to the sidelines.
"The word rotation frustrates me, it's more about player management," he said.
"We feel we've made the right decision for this Test match and also for Mitch (Starc)."
Sri Lanka made one change, bringing in Dhammika Prasad for injured new ball bowler Nuwan Kulasekara.
At the toss Jayawardene said was delighted to be batting in the "brilliant" batting conditions.
Australia: Ed Cowan, David Warner, Phil Hughes, Shane Watson, Michael Clarke, Mike Hussey, Matthew Wade, Mitchell Johnson, Peter Siddle, Nathan Lyon, Jackson Bird.
Sri Lanka: Tillakaratne Dilshan, Dimuth Karunaratne, Kumar Sangakkara, Mahela Jayawardene (capt), Thilan Samaraweera, Angelo Mathews, Prasanna Jayawardene, Dhammika Prasad, Rangana Herath, Shaminda Eranga, Chanaka Welegedara.
Read more at The Australian.