Johnson starred in his side's 281-run win over South Africa in the first Test with 12 wickets, but Siddle (three wickets), Ryan Harris and Nathan Lyon (both two) also contributed.
MORE: Second Test Preview: South Africa v Australia | Mitchell Johnson blow sidelines Ryan McLaren
Siddle, 29, said the left-armer's stunning form was making it easier for every bowler in Australia's attack.
"It's always nice to have someone who's bowling so well and building so much pressure on the batsman that they get to the other end, their footwork is a bit shaky and we can make the most of that," he said ahead of the second Test starting in Port Elizabeth on Thursday.
"You can build a bit more pressure the way I bowl with a certain plan, rather than trying to blast the batsmen out when I am bowling with him. It probably does change my approach a little bit."
In a Test series billed as a battle between the world's two best bowling attacks, Australia got the early upper-hand.
South Africa paceman Vernon Philander could only take 1-97, struggling to support star team-mate Dale Steyn.
Siddle praised his team's batsmen for putting pressure on Philander and said staying on top was the key to keeping the 28-year-old quiet.
"He's probably a bloke that thrives on conditions and obviously the batters made the most of it the other day and backed themselves to play with a bit of confidence," he said.
"A lot of teams have sat back and let him build the pressure on them, which has got him wickets.
"The way the boys attacked him and approached him the other day, getting off strike and swapping left and right-handers, that puts the pressure back on him rather than him building all that pressure.
"The boys have learnt how to play him. We're not sitting back and worried about what he's going to bring."