The combination of Johnson's 12 wickets and his fearsome helmet strikes to Hashim Amla and Ryan McLaren in Australia's crushing 281-run win over South Africa enhanced the left-hander's rapidly burgeoning reputation.

But Smith, who was out twice from a total of six balls from Johnson, was less impressed.

''I think the surface suited his style of bowling here,'' Smith said.

''He got a lot of difficult bounce, he got a lot of balls to get really big on batters in good areas, which made it obviously very tough. But it's not long ago that we can think back to big moments in games where we've been able to put him under pressure.

''Obviously he's bowling well, [but] I truly believe that the wicket played a big role in the success that he had. The stats, even in the Ashes, say that he picked up a lot of lower-order wickets.''

The pitch for the second Test at Port Elizabeth may not be quite as lively, but Smith's comments are sure to fire Johnson up - and ominously for the South Africans, he expects to get better.

''I said to Michael [Clarke] after the first innings that there was definitely room for improvement,'' Johnson said.

Johnson's 12-127 were the best figures by any Test paceman since Indian Irfan Pathan's 12-126 against Zimbabwe in September 2005.

His seven-wicket effort in the first innings was rated by his coach, Darren Lehmann, as the most dangerous he had seen. In the second he claimed another five, including both Proteas' openers within his first two overs, to finish with his career-best figures.

On the final day of the Test, Johnson struck two telling blows. The first was when he hit Amla, the world's No.2 Test batsman, in the helmet with a fiercely rearing delivery, the first he had faced. The second involved left-hander McLaren being unable to evade a bouncer and instead ducking into a ball that clattered into his helmet so hard it could be clearly heard from the open-air media box at the other end of the ground.

It took about five minutes for staff to successfully stem the bleeding created by the blow, which occurred even though he was wearing a helmet.

''It looks like he's been scrumming for three days … before the Super 15s,'' Smith said, comparing the wound to a rugby union grappling injury. ''But he's all right. He's a tough boy.''

Clarke declined to suggest the South African batsmen were mentally scarred by Johnson having bounced out so many of them, instead lauding the paceman.

''I don't know what South Africa is feeling right now,'' he said. ''I know there is not one cricket lover around the world that doesn't know Mitchell Johnson is bowling at 150km/h and executing his skills better than any other bowler in the world.

''Whether you play the game or watch the game, you know. They've seen it against England. He showed it here again in different conditions. He's bowling fast.

''He's the fastest bowler in the world at the moment, there's no doubt about it, but his execution and his skills are as good as any other bowler's.''

Since Australia's home Ashes series began Johnson has taken 49 wickets in six Tests, which has triggered his bowling average to plummet - a legitimate description given he has played 57 Tests - from 30.93 to 27.5.

Johnson's four man-of-the-match awards from those six Tests, which included the award from the just completed Centurion Park Test, has lifted him to seventh in Australia's tally since awards have been consistently given since the mid-1980s. The only player to have won at least five awards with a better strike rate than Johnson's one every 6.3 matches is Pakistan legend Wasim Akram, who claimed 17 from 104 Tests (one every 6.1).

Johnson expressed his satisfaction at being able to maintain the ''fear factor'' that helped bring him wickets during the Ashes.

''Playing away from home that's where you really can test yourself,'' he said.

''We're up against the No.1 side so I think that's good motivation for us to just keep getting better.

''It makes me feel proud inside and … is something that I will look back on at the end of my career and be proud of that moment. But for now it is only one Test match and we have two to come.''

Lehmann said he had no fear that Johnson would be any less effective in Port Elizabeth, on a pitch that typically favours spin, because of his transition at the start of the Ashes from the Gabba to the batsman-friendly conditions in Adelaide, where he took 8-113. ''He was really effective in Adelaide when it was a flatter wicket and reversed a bit,'' Lehmann said.