Australia's Mitchell Johnson has claimed that he has found his best form ahead of the first Ashes Test in Cardiff.

Before the announcement that Ryan Harris had retired from cricket due to his injury troubles, reports had suggested that Harris, Johnson and Josh Hazlewood were battling for two places in the side.

However, Johnson looks certain to play a key role in the series as Australia prepare for Wednesday's opening exchange between the two sides, and he is confident of delivering the goods after leading the way in the 2013-14 whitewash over England.

"It's very close now and the excitement definitely goes up another notch, we're all excited. It's been a big couple of days with Ryan Harris retiring, he's a good mate of mine and a fellow fast bowler," the 33-year-old told Sky Sports News.

"I'm feeling really good, really confident. [I] feel I'm bowling the best that I can at the moment. I've been really happy at the way the ball has come out, nice swing, nice pace. It's always competitive in the nets. I enjoy that part of it but I want to get out there and play the real stuff."

Johnson took 37 wickets in the 2013-14 Ashes to clinch the man of the series award.