|Tour match, Canterbury, day three of four|
|Australia 507-8 (dec) & 322-4 M Marsh 101, Watson 81, Clarke 47|
|Kent 280: Key 87, Denly 36; Johnson 4-56|
Mitchell Marsh scored a rapid century as Australia built a commanding lead of 549 on the third day of their tour match against Kent.
The 23-year-old, who is vying with Shane Watson for the Ashes all-rounder berth, brought his hundred up off 93 balls, including five sixes, before retiring on 101.
Watson himself made a 76-ball 81 as Australia reached 322-4 at stumps.
Kent began the day on 203-5 but lost their last five wickets for 77 runs.
Fast bowler Ryan Harris, who has not played a test since January, took his first wickets of the tour.
He had England limited-overs batsman Sam Billings caught behind by Brad Haddin for 24, before Adam Ball holed out to Peter Siddle for 45.
Mitchell Marsh then caught and bowled Mitchell Claydon, before Johnson uprooted Adam Riley's middle stump with the first ball of his second spell.
Ivan Thomas eventually fell for 13 to spinner Fawad Ahmed as Kent were all out for 280.
Australia captain Michael Clarke then decided against the follow-on and promoted himself up the order to opener, in place of Shaun Marsh, to partner Chris Rogers.
The pair's opening stand of 91 was broken when Rogers departed for 45, caught by substitute Sam Weller off Riley's bowling.
Clarke was Riley's second victim, falling for 47, as Australia reached 132-2 at tea.
Watson and Mitchell Marsh then put on a 153-run partnership as Australia upped the scoring rate.
Marsh's retirement and the wicket of Watson left Johnson and Brad Haddin at the crease at the close of play.