Brydon Coverdale is an assistant editor at ESPNcricinfo. He tweets here
There have been times in Mitchell Johnson's past as an erratic Ashes bowler when his emotions might have got the better of him, but not like they did on the final day at the WACA. Johnson was on the verge of tears as he shook the hands of England's batsmen and umpires in the moments immediately following his Ashes-sealing wicket of James Anderson. It was a cathartic day for several Australians, none more so than Johnson.
The subject of Barmy Army taunts in previous Ashes campaigns, Johnson had always struggled to live up to expectations against England, remembered more for his wayward spells than his challenging ones. But at 32, now a husband and father with a greater perspective on life and cricket, Johnson entered this series in a different state of mind. He has been, without question, Australia's most influential player in the series.
It is not just the wickets, although his tally of 23 at 15.47 and a strike-rate of a wicket every 33 balls is remarkable. It has been his pace, accuracy and consistency that has troubled England over the first three Tests. If England were metaphorically on the back foot coming to Perth, it was largely because Johnson had literally forced them on to the back foot in the first two Tests. It was fitting that he took the wicket that confirmed the triumph.
It might easily have ended differently for Johnson, for one of the ugliest sights of the whole series came on the final day at the WACA when Johnson tried to do the team thing and cut off a boundary at deep square leg. His awkward slide was vividly reminiscent of Simon Jones' slide at the Gabba in 2002-03, which resulted in a ruptured cruciate ligament. Johnson's right knee jolted with such force in the WACA turf that viewers turned away from replays.
Johnson was fortunate that a dirty set of whites was the worst that resulted of it and after a few stretches he returned to the top of his mark to bowl the next over. After a change of trousers at the lunch break, Johnson was back on the field to wrap up Australia's victory.
"I think Mitch has known his role from the start of this series," Michael Clarke, the captain, said. "He's known what I've expected of him in this team at the moment with other bowlers around him. And credit to the other guys, because I think they've played a big part to allow Mitch to bowl the way he has bowled.
"But this game was a really good example. Mitch's pace probably wasn't as high as it was in the first two Test matches, but he executed with skill, and he's got natural variation. You saw there he got a wicket with the slower ball as well. He was able to bowl good areas. That's the class of Mitchell Johnson. Through his career he's been used in different situations. He's bowled long spells. He's opened the bowling. He's bowled first change. He can do all of that.
"It's just about what is best for the team. It's just another example of players putting the team first. He's been happy to bowl in short spells and maximise his pace, and then throughout this Test match at times he's had to bowl longer spells and be more consistent, and he's able to do that, which is very pleasing."
Johnson finished with match figures of 6 for 140 at the WACA to give him 23 for the series. England's two main strike bowlers, Anderson and Stuart Broad, haven't even taken that many between them. England's captain, Alastair Cook, said his men had always known that Johnson could provide a serious threat when in form, but they had been surprised by his control and lack of loose balls this time around.
"We've known that when Mitch gets it right, he's a very good bowler," Cook said. "Even when he was having that tough series in 2010-11, when he got it right here in Perth he [proved he] was a tough bowler to face. He bowls quickly and swings it, and that's a pretty good combination. 230-odd wickets suggests he's done it for a fair period of time. When he gets it right he's dangerous.
"It hasn't surprised that he's taken wickets, but I think it's surprised us the control he's had. He's managed to improve his control a lot since the last time we saw him."