"Even in the last test match, Michael didn't bowl me - in one spell especially - when I could have bowled," Watson said when asked why he bowled only nine overs in the innings.
"He was more so just giving me a chance to be as fresh as I could going into that second innings in the batting side of things.
"It just gives me that time to physically be able to just freshen up but also mentally.
"A couple of times, I was still caught up in my bowling side of things when I've gone out to bat and got out very early.
"At least it gives me that time to be able to reflect on how things have panned out with the ball and realign to be able to make sure I get it right with the bat. I think this is more a permanent move - I hope, anyway.
"I certainly enjoyed opening but it meant I wasn't really able to bowl that much really, considering I was going to have to go in and take the first ball.
"Four hopefully will suit me really well."
Australia have left out Mitchell Johnson for the first test.
Pace bowlers Peter Siddle and Ben Hilfenhaus return after being rested from the third test against South Africa in Perth.
Johnson was named 12th man, with young fellow left-arm quick Mitchell Starc retaining his place for the Bellerive Oval test after taking eight wickets in Perth.
Johnson was impressive at the WACA Ground, claiming six wickets in his first test appearance for 12 months.
"Mitchell bowled very well in Perth and he is unlucky to miss out," said Clarke.
"Sidds and Hilf come back into the team as two guys who have performed very well for us over the last 12 months, both being fully fit.
"All four guys have performed really well. It certainly wasn't a simple decision."
- AAP
